Use the Prescribed Motion subnode to prescribe the relative motion on a joint. You can also prescribe the motion by giving the time derivatives of the joint degrees of freedom, for example, velocity for translation motion and angular velocity for rotational motion. Activation conditions can be used to prescribe the motion for only a certain duration. Axis directions are interpreted in the selected coordinate system.
The Prescribed Motion subnode can be added to the
Prismatic Joint,
Hinge Joint,
Cylindrical Joint,
Screw Joint,
Planar Joint,
Ball Joint,
Slot Joint, and
Reduced Slot Joint. The contents of the settings sections will differ between different joint types
Select an Activation condition —
Always active or
Conditionally active. For
Conditionally active enter a
Deactivation indicator expression iup. For the joints having more than one degree of freedom (Cylindrical Joint, Screw Joint, Planar Joint, Slot Joint, and Reduced Slot Joint),
Never active is also an option.
For the Planar Joint, enter values or expressions for the
Initial prescribed motion axis ep0.
For the Ball Joint and
Slot Joint, enter values or expressions for the
Initial prescribed motion axis ep0.
Select an Activation condition —
Always active or
Conditionally active. For
Conditionally active enter a
Deactivation indicator expression iθp. (In this case, the variable name is
iφp for the Ball Joint and Slot Joint). For the joints having more than one degree of freedom (Cylindrical Joint, Screw Joint, Planar Joint, Slot Joint, and Reduced Slot Joint),
Never active is also an option.
Select Evaluate reaction forces to compute the reaction force caused by the prescribed motion. The default is to not compute the reaction force. When selected, the prescribed motion is implemented as a weak constraint. If the prescribed motion is not active all through the study step, because
Activation condition is
Conditionally active, this setting is ignored. Reaction forces are never computed in that case.
Select Apply reaction only on joint variables to use a unidirectional constraint for enforcing the prescribed motion. The default is that bidirectional constraints are used. This setting is useful in a situation where a bidirectional constraint would give an unwanted coupling in the equations. This would happen if the prescribed value of the motion is a variable solved for in other equations.
Physics tab with Prismatic Joint,
Hinge Joint,
Cylindrical Joint,
Screw Joint,
Planar Joint,
Ball Joint,
Slot Joint, or
Reduced Slot Joint selected in the model tree:
Attributes>Prescribed Motion
for the Ball Joint and Slot Joint.