Nonholonomic system
Encyclopedia
A nonholonomic system in physics
and mathematics
is a system
whose state depends on the path taken to achieve it. Such a system is described by a set of parameter
s subject to differential constraints, such that when the system evolves along a path in its parameter space
(the parameters varying continuously in values) but finally returns to the original set of values at the start of the path, the system itself may not have returned to its original state.
More precisely, a nonholonomic system, also called an anholonomic system, is one in which there is a continuous closed circuit of the governing parameters, by which the system may be transformed from any given state to any other state. Because the final state of the system depends on the intermediate values of its trajectory through parameter space, the system can not be represented by a conservative potential function
as can, for example, the inverse square law of the gravitational force. This latter is an example of a holonomic system: path integrals in the system depend only upon the initial and final states of the system (positions in the potential), completely independent of the trajectory of transition between those states. The system is therefore said to be integrable, while the nonholonomic system is said to be nonintegrable. When a path integral is computed in a nonholonomic system, the value represents a deviation within some range of admissible values and this deviation is said to be an anholonomy produced by the specific path under consideration. This term was introduced by Heinrich Hertz in 1894.
The general character of anholonomic systems is that of implicitly dependent parameters. If the implicit dependency can be removed, for example by raising the dimension of the space, thereby adding at least one additional parameter, the system is not truly nonholonomic, but is simply incompletely modeled by the lower dimensional space. In contrast, if the system intrinsically can not be represented by independent coordinates (parameters), then it is truly an anholonomic system. Some authors make much of this by creating a distinction between so-called internal and external states of the system, but in truth, all parameters are necessary to characterize the system, be they representative of "internal" or "external" processes, so the distinction is in fact artificial. However, there is a very real and irreconcilable difference between physical systems that obey conservation principles and those that do not. In the case of parallel transport
on a sphere, the distinction is clear: a Riemannian manifold
has a metric fundamentally distinct from that of a Euclidean space
. For parallel transport on a sphere, the implicit dependence is intrinsic to the non-euclidean metric. The surface of a sphere is a two dimensional space. By raising the dimension, we can more clearly see the nature of the metric, but it is still fundamentally a two dimensional space with parameters irretrievably entwined in dependency by the Riemannian metric.
. In the local coordinate frame the pendulum is swinging in a vertical plane with a particular orientation with respect to geographic north at the outset of the path. The implicit trajectory of the system is the line of latitude on the earth where the pendulum is located. Even though the pendulum is stationary in the earth frame, it is moving in a frame referred to the sun and rotating in synchrony with the Earth's rate of revolution, so that the only apparent motion of the pendulum is that caused by the rotation of the earth. This latter frame is considered to be an inertial reference frame, although it too is non-inertial in more subtle ways. The earth frame is well known to be non-inertial, a fact made perceivable by the apparent presence of centrifugal and Coriolis
forces.
Motion along the line of latitude is parameterized by the passage of time, and the Foucault pendulum's plane of oscillation appears to rotate about the local vertical axis as time passes. The angle of rotation of this plane at a time t with respect to the initial orientation is the anholonomy of the system. The anholonomy induced by a complete circuit of latitude is proportional to the solid angle
subtended by that circle of latitude. The path need not be constrained to latitude circles. For example, the pendulum might be mounted in an airplane. The anholonomy is still proportional to the solid angle subtended by the path, which may now be quite irregular. The Foucault pendulum is a physical example of parallel transport
.
The sphere may now be rolled along any continuous closed path in the z=0 plane, not necessarily a simply connected path, in such a way that it neither slips nor twists, so that C returns to x=0, y=0, z=1. In general, point B is no longer coincident with the origin, and point R no longer extends along the positive x axis. In fact, by selection of a suitable path, the sphere may be re-oriented relative the initial orientation to any possible orientation of the sphere with C located at x=0, y=0, z=1. (reference: The Nonholonomy of the Rolling Sphere, Brody Dylan Johnson, The American Mathematical Monthly, June-July 2007, vol. 114, pp. 500–508) The system is therefore nonholonomic. The anholonomy may be represented by the doubly unique quaternion
(q and -q) which, when applied to the points that represent the sphere, carries points B and R to their new positions.
Now, coil the fiber tightly around a cylinder ten centimeters in diameter. The path of the fiber now describes a helix
which, like the circle, has constant curvature
. The helix also has the interesting property of having constant torsion
. As such the result is a gradual rotation of the fiber about the fiber's axis as the fiber's centerline progresses along the helix. Correspondingly, the stripe also twists about the axis of the helix.
When linearly polarized light is again introduced at one end, with the orientation of the polarization aligned with the stripe, it will, in general, emerge as linear polarized light aligned not with the stripe, but at some fixed angle to the stripe, dependent upon the length of the fiber, and the pitch and radius of the helix. This system is also nonholonomic, for we can easily coil the fiber down in a second helix and align the ends, returning the light to its point of origin. The anholonomy is therefore represented by the deviation of the angle of polarization with each circuit of the fiber. By suitable adjustment of the parameters, it is clear that any possible angular state can be produced.
In order for the above form to be nonholonomic, it is also required that the left hand side neither be a total differential nor be able to be converted into one, perhaps via an integrating factor
.
For virtual displacements only, the differential form of the constraint is
a system is non-holonomic if the controllable degrees of freedom are less than the total degrees of freedom.
Refer to holonomic robotics for a more detailed description.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
and mathematics
Mathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
is a system
System
System is a set of interacting or interdependent components forming an integrated whole....
whose state depends on the path taken to achieve it. Such a system is described by a set of parameter
Parameter
Parameter from Ancient Greek παρά also “para” meaning “beside, subsidiary” and μέτρον also “metron” meaning “measure”, can be interpreted in mathematics, logic, linguistics, environmental science and other disciplines....
s subject to differential constraints, such that when the system evolves along a path in its parameter space
Parameter space
In science, a parameter space is the set of values of parameters encountered in a particular mathematical model. Often the parameters are inputs of a function, in which case the technical term for the parameter space is domain of a function....
(the parameters varying continuously in values) but finally returns to the original set of values at the start of the path, the system itself may not have returned to its original state.
More precisely, a nonholonomic system, also called an anholonomic system, is one in which there is a continuous closed circuit of the governing parameters, by which the system may be transformed from any given state to any other state. Because the final state of the system depends on the intermediate values of its trajectory through parameter space, the system can not be represented by a conservative potential function
Potential function
The term potential function may refer to:* A mathematical function whose values are a physical potential.* The class of functions known as harmonic functions, which are the topic of study in potential theory.* The potential function of a potential game....
as can, for example, the inverse square law of the gravitational force. This latter is an example of a holonomic system: path integrals in the system depend only upon the initial and final states of the system (positions in the potential), completely independent of the trajectory of transition between those states. The system is therefore said to be integrable, while the nonholonomic system is said to be nonintegrable. When a path integral is computed in a nonholonomic system, the value represents a deviation within some range of admissible values and this deviation is said to be an anholonomy produced by the specific path under consideration. This term was introduced by Heinrich Hertz in 1894.
The general character of anholonomic systems is that of implicitly dependent parameters. If the implicit dependency can be removed, for example by raising the dimension of the space, thereby adding at least one additional parameter, the system is not truly nonholonomic, but is simply incompletely modeled by the lower dimensional space. In contrast, if the system intrinsically can not be represented by independent coordinates (parameters), then it is truly an anholonomic system. Some authors make much of this by creating a distinction between so-called internal and external states of the system, but in truth, all parameters are necessary to characterize the system, be they representative of "internal" or "external" processes, so the distinction is in fact artificial. However, there is a very real and irreconcilable difference between physical systems that obey conservation principles and those that do not. In the case of parallel transport
Parallel transport
In geometry, parallel transport is a way of transporting geometrical data along smooth curves in a manifold. If the manifold is equipped with an affine connection , then this connection allows one to transport vectors of the manifold along curves so that they stay parallel with respect to the...
on a sphere, the distinction is clear: a Riemannian manifold
Riemannian manifold
In Riemannian geometry and the differential geometry of surfaces, a Riemannian manifold or Riemannian space is a real differentiable manifold M in which each tangent space is equipped with an inner product g, a Riemannian metric, which varies smoothly from point to point...
has a metric fundamentally distinct from that of a Euclidean space
Euclidean space
In mathematics, Euclidean space is the Euclidean plane and three-dimensional space of Euclidean geometry, as well as the generalizations of these notions to higher dimensions...
. For parallel transport on a sphere, the implicit dependence is intrinsic to the non-euclidean metric. The surface of a sphere is a two dimensional space. By raising the dimension, we can more clearly see the nature of the metric, but it is still fundamentally a two dimensional space with parameters irretrievably entwined in dependency by the Riemannian metric.
The Foucault Pendulum
The classic example of a nonholonomic system is the Foucault pendulumFoucault pendulum
The Foucault pendulum , or Foucault's pendulum, named after the French physicist Léon Foucault, is a simple device conceived as an experiment to demonstrate the rotation of the Earth. While it had long been known that the Earth rotated, the introduction of the Foucault pendulum in 1851 was the...
. In the local coordinate frame the pendulum is swinging in a vertical plane with a particular orientation with respect to geographic north at the outset of the path. The implicit trajectory of the system is the line of latitude on the earth where the pendulum is located. Even though the pendulum is stationary in the earth frame, it is moving in a frame referred to the sun and rotating in synchrony with the Earth's rate of revolution, so that the only apparent motion of the pendulum is that caused by the rotation of the earth. This latter frame is considered to be an inertial reference frame, although it too is non-inertial in more subtle ways. The earth frame is well known to be non-inertial, a fact made perceivable by the apparent presence of centrifugal and Coriolis
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...
forces.
Motion along the line of latitude is parameterized by the passage of time, and the Foucault pendulum's plane of oscillation appears to rotate about the local vertical axis as time passes. The angle of rotation of this plane at a time t with respect to the initial orientation is the anholonomy of the system. The anholonomy induced by a complete circuit of latitude is proportional to the solid angle
Solid angle
The solid angle, Ω, is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large that object appears to an observer looking from that point...
subtended by that circle of latitude. The path need not be constrained to latitude circles. For example, the pendulum might be mounted in an airplane. The anholonomy is still proportional to the solid angle subtended by the path, which may now be quite irregular. The Foucault pendulum is a physical example of parallel transport
Parallel transport
In geometry, parallel transport is a way of transporting geometrical data along smooth curves in a manifold. If the manifold is equipped with an affine connection , then this connection allows one to transport vectors of the manifold along curves so that they stay parallel with respect to the...
.
The Rolling Sphere
This example is very easy for the reader to demonstrate. Consider a three dimensional orthogonal Cartesian coordinate frame, for example a level table top with a point marked on it for the origin, and the x and y axes laid out with pencil lines. Take a sphere of unit radius, for example a ping pong ball, and mark one point B in blue. Corresponding to this point is a diameter of the sphere, and the plane orthogonal to this diameter positioned at the center C of the sphere defines a great circle called the equator associated with point B. On this equator, select another point R and mark it in red. Position the sphere on the z=0 plane such that the point B is coincident with the origin, C is located at x=0, y=0, z=1, and R is located at x=1, y=0, and z=1, i.e. R extends in the direction of the positive x axis. This is the initial or reference orientation of the sphere.The sphere may now be rolled along any continuous closed path in the z=0 plane, not necessarily a simply connected path, in such a way that it neither slips nor twists, so that C returns to x=0, y=0, z=1. In general, point B is no longer coincident with the origin, and point R no longer extends along the positive x axis. In fact, by selection of a suitable path, the sphere may be re-oriented relative the initial orientation to any possible orientation of the sphere with C located at x=0, y=0, z=1. (reference: The Nonholonomy of the Rolling Sphere, Brody Dylan Johnson, The American Mathematical Monthly, June-July 2007, vol. 114, pp. 500–508) The system is therefore nonholonomic. The anholonomy may be represented by the doubly unique quaternion
Quaternion
In mathematics, the quaternions are a number system that extends the complex numbers. They were first described by Irish mathematician Sir William Rowan Hamilton in 1843 and applied to mechanics in three-dimensional space...
(q and -q) which, when applied to the points that represent the sphere, carries points B and R to their new positions.
Linear Polarized Light in an Optical Fiber
Take a length of optical fiber, say three meters, and lay it out in an absolutely straight line. When a vertically polarized beam is introduced at one end, it emerges from the other end, still polarized in the vertical direction. Mark the top of the fiber with a stripe, corresponding with the orientation of the vertical polarization.Now, coil the fiber tightly around a cylinder ten centimeters in diameter. The path of the fiber now describes a helix
Helix
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...
which, like the circle, has constant curvature
Curvature
In mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat, or straight in the case of a line, but this is defined in different ways depending on the context...
. The helix also has the interesting property of having constant torsion
Torsion
The word torsion may refer to the following:*In geometry:** Torsion of a curve** Torsion tensor in differential geometry** The closely related concepts of Reidemeister torsion and analytic torsion ** Whitehead torsion*In algebra:** Torsion ** Tor functor* In medicine:** Ovarian...
. As such the result is a gradual rotation of the fiber about the fiber's axis as the fiber's centerline progresses along the helix. Correspondingly, the stripe also twists about the axis of the helix.
When linearly polarized light is again introduced at one end, with the orientation of the polarization aligned with the stripe, it will, in general, emerge as linear polarized light aligned not with the stripe, but at some fixed angle to the stripe, dependent upon the length of the fiber, and the pitch and radius of the helix. This system is also nonholonomic, for we can easily coil the fiber down in a second helix and align the ends, returning the light to its point of origin. The anholonomy is therefore represented by the deviation of the angle of polarization with each circuit of the fiber. By suitable adjustment of the parameters, it is clear that any possible angular state can be produced.
Constraints
A nonholonomic constraint has the form given below and is nonintegrable:
-
is the number of coordinates.
is the number of constraint equations.
are coordinates.
are coefficients.
In order for the above form to be nonholonomic, it is also required that the left hand side neither be a total differential nor be able to be converted into one, perhaps via an integrating factor
Integrating factor
In mathematics, an integrating factor is a function that is chosen to facilitate the solving of a given equation involving differentials. It is commonly used to solve ordinary differential equations, but is also used within multivariable calculus, in this case often multiplying through by an...
.
For virtual displacements only, the differential form of the constraint is
Robotics
In roboticsRobotics
Robotics is the branch of technology that deals with the design, construction, operation, structural disposition, manufacture and application of robots...
a system is non-holonomic if the controllable degrees of freedom are less than the total degrees of freedom.
Refer to holonomic robotics for a more detailed description.
See also
- Anholonomic
- Bicycle and motorcycle dynamicsBicycle and motorcycle dynamicsBicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics is a branch of classical mechanics, which in turn is a branch of physics. Bike motions of interest include balancing, steering, braking,...
- Falling cat problemFalling cat problemThe falling cat problem consists of explaining the underlying physics behind the common observation of the cat righting reflex: how a free-falling cat can turn itself right-side-up as it falls, no matter which way up it was initially, without violating the law of conservation of angular...
- HolonomicHolonomicIn mathematics and physics, the term holonomic may occur with several different meanings.-Holonomic basis:A holonomic basis for a manifold is a set of basis vectors ek for which all Lie derivatives vanish:[e_j,e_k]=0 \,...
- Parallel parking problemParallel parking problemThe parallel parking problem is a motion planning problem in control theory and mechanics to determine the path a car must take in order to parallel park into a parking space. The front wheels of a car are permitted to turn, but the rear wheels must stay fixed...
- Pfaffian constraintPfaffian constraintIn robot motion planning, a Pfaffian constraint is a set of k linearly independent constraints linear in velocity, i.e., of the formA \dot q=0One source of Pfaffian constraints is rolling without slipping in wheeled robots....
Variational principles for nonholonomic systems
- V.V. Rumiantsev, "On Hamilton's principle for nonholonomic systems" Journal of Applied Mathematics and Mechanics 42(3), (1978) 407-419.
- V.V. Rumyantsev, "Forms of Hamilton’s principle for nonholonomic systems" Facta Universitatis. Series Mechanics, Automatic Control and Robotics 2(19), (2000) 1035-1048.
- V.V. Rumiantsev, "On integral principles for nonholonomic systems" Journal of Applied Mathematics and Mechanics 46(1), (1982) 1-8.