SimTK::Motion Class Reference

A Motion object belongs to a particular mobilizer and specifies how the associated motion is to be calculated. More...

#include <Motion.h>

Inheritance diagram for SimTK::Motion:

List of all members.

Classes
class	Custom
	This class can be used to define new motions. More...
class	Sinusoid
	Prescribe position, velocity, or acceleration motion as a sinusoidal function of time, m(t) = a * sin( w*t + p ). More...
class	Steady
	This non-holonomic Motion object imposes a constant rate on all mobilities. More...
Public Types
enum	Level { Acceleration = 0, Velocity = 1, Position = 2 }
	What is the highest level of motion that is driven? Lower levels are also driven; higher levels are determined by integration. More...
enum	Method {   Zero = 0, Discrete = 1, Prescribed = 2, Free = 3,   Fast = 4 }
	There are several ways to specify the motion at this Level, and the selected method also determines lower-level motions. More...
Public Member Functions
	Motion ()
	Motion (MotionImpl *r)
const MobilizedBody &	getMobilizedBody () const
	Get the MobilizedBody to which this Motion belongs.
Level	getLevel (const State &) const
Method	getLevelMethod (const State &) const
void	calcAllMethods (const State &s, Method &qMethod, Method &uMethod, Method &udotMethod) const
Static Public Member Functions
static const char *	nameOfLevel (Level)
	Returns a human-readable name corresponding to the given Level; useful for debugging.
static const char *	nameOfMethod (Method)
	Returns a human-readable name corresponding to the given Method; useful for debugging.

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Detailed Description

A Motion object belongs to a particular mobilizer and specifies how the associated motion is to be calculated.

There are two independent aspects: (1) at what level is the motion driven (low to high: acceleration, velocity, or position), and (2) how is the motion at that level specified. Levels lower than the driven level are also driven; higher levels are free and determined by integration. This table shows the possibilities:

     Level How driven    Acceleration    Velocity      Position
     ----- ----------    ------------    ----------    ----------
      Acc  Zero               0           discrete       free
       "   Discrete        discrete         free           "
       "   Prescribed      a(t,q,u)          "             "
       "   Free           from forces        "             "

      Vel  Zero               0              0          discrete
       "   Discrete           0           discrete        free
       "   Prescribed       dv/dt          v(t,q)          "
       "   Fast               0           relax(v)         "

      Pos  Zero               0              0           0 (ref.)
       "   Discrete           0              0          discrete
       "   Prescribed      d2p/dt2         dp/dt          p(t)
       "   Fast               0              0          relax(p)

There are two duplicates in the above table: specifying acceleration as Zero is the same as specifying velocity as Discrete and specifying velocity as Zero is the same as specifying position as Discrete.

For mobilizers with more than one mobility, the associated Motion controls all the mobilities and moreover they are all driven at the same level and by the same method. TODO?: provide Motion::Composite for building up a Motion from individual axis specifications.

Motion is a PIMPL-style abstract base class, with concrete classes defined for each kind of Motion. There is a set of built-in Motions and a generic "Custom" Motion (an abstract base class) from which advanced users may derive their own Motion objects.

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Member Enumeration Documentation

enum SimTK::Motion::Level

What is the highest level of motion that is driven? Lower levels are also driven; higher levels are determined by integration.

Enumerator:

Acceleration	we know udot; integrate to get u, q
Velocity	we know u and udot; integrate to get q
Position	we know q, u, and udot

enum SimTK::Motion::Method

There are several ways to specify the motion at this Level, and the selected method also determines lower-level motions.

Free is only permitted when Level==Acceleration, and Fast is not allowed for that Level.

Enumerator:

Zero
Discrete	motion is "slow"; lower levels are zero
Prescribed	motion is function of time and state; <level is derivative
Free	accel. calculated from forces, pos and vel integrated
Fast	motion is "fast"; lower levels are zero

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Constructor & Destructor Documentation

SimTK::Motion::Motion

(

)

[inline]

SimTK::Motion::Motion

(

MotionImpl *

r

)

[inline, explicit]

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Member Function Documentation

static const char* SimTK::Motion::nameOfLevel

(

Level

)

[static]

Returns a human-readable name corresponding to the given Level; useful for debugging.

If the Level is unrecognized the method will return some text to that effect rather than crashing.

static const char* SimTK::Motion::nameOfMethod

(

Method

)

[static]

Returns a human-readable name corresponding to the given Method; useful for debugging.

If the Method is unrecognized the method will return some text to that effect rather than crashing.

const MobilizedBody& SimTK::Motion::getMobilizedBody

(

)

const

Get the MobilizedBody to which this Motion belongs.

Level SimTK::Motion::getLevel

(

const State &

)

const

Method SimTK::Motion::getLevelMethod

(

const State &

)

const

void SimTK::Motion::calcAllMethods	(	const State &	s,
		Method &	qMethod,
		Method &	uMethod,
		Method &	udotMethod
	)		const [inline]

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The documentation for this class was generated from the following file:

• Motion.h