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Simbody
3.4 (development)
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Simbody
3.4 (development)
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Enforce that a fixed station on one body remains coincident with a fixed station on a second body, as though there were a ball joint connecting them at those points. More...
#include <Constraint.h>
Inheritance diagram for SimTK::Constraint::Ball:Public Member Functions | |
| Ball (MobilizedBody &body1, MobilizedBody &body2) | |
| Connect the origin of body1 to the origin of body2. | |
| Ball (MobilizedBody &body1, const Vec3 &defaultPoint1, MobilizedBody &body2, const Vec3 &defaultPoint2) | |
| Connect body1 and body2 at given station points, given in the body frame of the corresponding body. | |
| Ball () | |
| Default constructor creates an empty handle. | |
| void | setPointOnBody1 (State &state, const Vec3 &point_B1) const |
| Change the station point on body 1 at which this Constraint acts. | |
| void | setPointOnBody2 (State &state, const Vec3 &point_B2) const |
| Change the station point on body 2 at which this Constraint acts. | |
| const Vec3 & | getPointOnBody1 (const State &state) const |
| Return from the given state the constrained station on body 1, in the body 1 frame. | |
| const Vec3 & | getPointOnBody2 (const State &state) const |
| Return from the given state the constrained station on body 2, in the body 2 frame. | |
| Ball & | setDefaultPointOnBody1 (const Vec3 &defaultPoint_B1) |
| Change the default station location on body 1. | |
| Ball & | setDefaultPointOnBody2 (const Vec3 &defaultPoint_B2) |
| Change the default station location on body 2. | |
| const Vec3 & | getDefaultPointOnBody1 () const |
| Return the default location for the station point on body 1, as a vector in the body 1 frame. | |
| const Vec3 & | getDefaultPointOnBody2 () const |
| Return the default location for the station point on body 2, as a vector in the body 2 frame. | |
| Ball & | setDefaultRadius (Real r) |
| For visualization only, you can override the default radius used by this Constraint to draw itself. | |
| Real | getDefaultRadius () const |
| Retreive the radius being used for visualization of this Constraint. | |
| MobilizedBodyIndex | getBody1MobilizedBodyIndex () const |
| Return the MobilizedBodyIndex corresponding to body 1. | |
| MobilizedBodyIndex | getBody2MobilizedBodyIndex () const |
| Return the MobilizedBodyIndex corresponding to body 2. | |
| Vec3 | getPositionErrors (const State &state) const |
| Return the current position-level constraint error for this Constraint. | |
| Vec3 | getVelocityErrors (const State &state) const |
| Return the current velocity-level constraint error for this Constraint. | |
| Vec3 | getAccelerationErrors (const State &) const |
| Return the current acceleration-level constraint error for this Constraint. | |
| Vec3 | getBallReactionForceOnBody1 (const State &) const |
| Return the force currently being applied by this Constraint to the point of body 1 that is coincident in space with the constrained point on body 2. | |
| Vec3 | getBallReactionForceOnBody2 (const State &) const |
| Return the force currently being applied by this Constraint to body 2, at its constrained station point. | |
| Vec3 | getMultipliers (const State &state) const |
| Return the three Lagrange multipliers associated with the three accleration-level constraint equations generated by this Constraint. | |
Enforce that a fixed station on one body remains coincident with a fixed station on a second body, as though there were a ball joint connecting them at those points.
Uses three position-level (holonomic) constraint equations to prevent relative translation in three orthogonal directions.
At construction you specify the two bodies to be connected by the Constraint, and give default values for a station on each body. The State is initialized with those default stations, but you can change them later.
The constraint is enforced by an internal (non-working) force applied at the spatial location of the point on body 2, on material points of each body that are coincident with that spatial location. Note that this is somewhat asymmetric when the ball is not properly assembled -- it acts as though the contact occurs at the point on body 2, not at the point on body 1. That is critical to ensure that Newton's 3rd law is satisified -- the action and reaction must occur at the same point.
The assembly condition is the same as the runtime constraint -- the two points can be brought together by driving the perr to zero.
| SimTK::Constraint::Ball::Ball | ( | MobilizedBody & | body1, |
| MobilizedBody & | body2 | ||
| ) |
Connect the origin of body1 to the origin of body2.
That is, the default stations will both be (0,0,0). You can change those later in the State using setPointOnBody1() and setPointOnBody2().
| SimTK::Constraint::Ball::Ball | ( | MobilizedBody & | body1, |
| const Vec3 & | defaultPoint1, | ||
| MobilizedBody & | body2, | ||
| const Vec3 & | defaultPoint2 | ||
| ) |
Connect body1 and body2 at given station points, given in the body frame of the corresponding body.
You can change those later in the State using setPointOnBody1() and setPointOnBody2().
| SimTK::Constraint::Ball::Ball | ( | ) | [inline] |
Default constructor creates an empty handle.
| void SimTK::Constraint::Ball::setPointOnBody1 | ( | State & | state, |
| const Vec3 & | point_B1 | ||
| ) | const |
Change the station point on body 1 at which this Constraint acts.
Provide the station location in the body 1 local frame. This overrides the default point that was supplied on construction. This is an Instance-stage change.
| void SimTK::Constraint::Ball::setPointOnBody2 | ( | State & | state, |
| const Vec3 & | point_B2 | ||
| ) | const |
Change the station point on body 2 at which this Constraint acts.
Provide the station location in the body 2 local frame. This overrides the default point that was supplied on construction. This is an Instance-stage change.
| const Vec3& SimTK::Constraint::Ball::getPointOnBody1 | ( | const State & | state | ) | const |
Return from the given state the constrained station on body 1, in the body 1 frame.
| const Vec3& SimTK::Constraint::Ball::getPointOnBody2 | ( | const State & | state | ) | const |
Return from the given state the constrained station on body 2, in the body 2 frame.
| Ball& SimTK::Constraint::Ball::setDefaultPointOnBody1 | ( | const Vec3 & | defaultPoint_B1 | ) |
Change the default station location on body 1.
This is a topological change meaning you'll have to call realizeTopology() again after changing the default point. If you want to change the constrained station during a simulation, use setPointOnBody1() instead to override it in a State.
| Ball& SimTK::Constraint::Ball::setDefaultPointOnBody2 | ( | const Vec3 & | defaultPoint_B2 | ) |
Change the default station location on body 2.
This is a topological change meaning you'll have to call realizeTopology() again after changing the default point. If you want to change the constrained station during a simulation, use setPointOnBody2() instead to override it in a State.
| const Vec3& SimTK::Constraint::Ball::getDefaultPointOnBody1 | ( | ) | const |
Return the default location for the station point on body 1, as a vector in the body 1 frame.
Note that this is not necessarily the station point being used for any given State; use getPointOnBody1() for that.
| const Vec3& SimTK::Constraint::Ball::getDefaultPointOnBody2 | ( | ) | const |
Return the default location for the station point on body 2, as a vector in the body 2 frame.
Note that this is not necessarily the station point being used for any given State; use getPointOnBody2() for that.
| Ball& SimTK::Constraint::Ball::setDefaultRadius | ( | Real | r | ) |
For visualization only, you can override the default radius used by this Constraint to draw itself.
| Real SimTK::Constraint::Ball::getDefaultRadius | ( | ) | const |
Retreive the radius being used for visualization of this Constraint.
Return the MobilizedBodyIndex corresponding to body 1.
Return the MobilizedBodyIndex corresponding to body 2.
| Vec3 SimTK::Constraint::Ball::getPositionErrors | ( | const State & | state | ) | const |
Return the current position-level constraint error for this Constraint.
This is the vector between the constrained stations on body 1 and body 2, which would be zero if this constraint were perfectly satisfied. The returned vector is measured in the Ancestor body frame. The given state must be realized through Position stage.
| Vec3 SimTK::Constraint::Ball::getVelocityErrors | ( | const State & | state | ) | const |
Return the current velocity-level constraint error for this Constraint.
This is the relative velocity between the material points of body 1 and body 2 that are coincident with the constrained station point on body 2; note that this is subtly different from the time derivative of the position error vector. The returned vector is measured in the Ancestor body frame. The given state must be realized through Velocity stage.
| Vec3 SimTK::Constraint::Ball::getAccelerationErrors | ( | const State & | ) | const |
Return the current acceleration-level constraint error for this Constraint.
This is the relative acceleration between the material points of body 1 and body 2 that are coincident with the constrained station point on body 2; this is precisely the time derivative of the velocity error vector (but not exactly the second time derivative of the position error). The returned vector is measured in the Ancestor body frame. The given state must be realized through Acceleration stage.
| Vec3 SimTK::Constraint::Ball::getBallReactionForceOnBody1 | ( | const State & | ) | const |
Return the force currently being applied by this Constraint to the point of body 1 that is coincident in space with the constrained point on body 2.
The force vector is expressed in body 1's local frame.
| Vec3 SimTK::Constraint::Ball::getBallReactionForceOnBody2 | ( | const State & | ) | const |
Return the force currently being applied by this Constraint to body 2, at its constrained station point.
The force vector is expressed in body 2's local frame.
| Vec3 SimTK::Constraint::Ball::getMultipliers | ( | const State & | state | ) | const |
Return the three Lagrange multipliers associated with the three accleration-level constraint equations generated by this Constraint.
Although these are related to reaction forces, if that's what you're interested in you should use getBallReactionForcesOnBody1() or getBallReactionForceOnBody2() instead; the definition of the multipliers is somewhat arbitrary and will not always be easy to interpret as forces. The given state must be realized through Acceleration stage.
1.7.6.1 
