WOLFRAM SYSTEM MODELER

# Universal

Universal joint (2 degrees-of-freedom, 4 potential states)

# Wolfram Language

In[1]:=
`SystemModel["Modelica.Mechanics.MultiBody.Joints.Universal"]`
Out[1]:=

# Information

This information is part of the Modelica Standard Library maintained by the Modelica Association.

Joint where frame_a rotates around axis n_a which is fixed in frame_a and frame_b rotates around axis n_b which is fixed in frame_b. The two frames coincide when "revolute_a.phi=0" and "revolute_b.phi=0". This joint has the following potential states;

• The relative angle phi_a = revolute_a.phi [rad] around axis n_a,
• the relative angle phi_b = revolute_b.phi [rad] around axis n_b,
• the relative angular velocity w_a (= der(phi_a)) and
• the relative angular velocity w_b (= der(phi_b)).

They are used as candidates for automatic selection of states from the tool. This may be enforced by setting "stateSelect=StateSelect.always" in the Advanced menu. The states are usually selected automatically. In certain situations, especially when closed kinematic loops are present, it might be slightly more efficient, when using the "StateSelect.always" setting.

In the following figure the animation of a universal joint is shown. The light blue coordinate system is frame_a and the dark blue coordinate system is frame_b of the joint (here: n_a = {0,0,1}, n_b = {0,1,0}, phi_a.start = 90o, phi_b.start = 45o).

# Parameters (6)

animation Value: true Type: Boolean Description: = true, if animation shall be enabled Value: {1, 0, 0} Type: Axis Description: Axis of revolute joint 1 resolved in frame_a Value: {0, 1, 0} Type: Axis Description: Axis of revolute joint 2 resolved in frame_b Value: world.defaultJointLength Type: Distance (m) Description: Length of cylinders representing the joint axes Value: world.defaultJointWidth Type: Distance (m) Description: Diameter of cylinders representing the joint axes Value: StateSelect.prefer Type: StateSelect Description: Priority to use joint coordinates (phi_a, phi_b, w_a, w_b) as states

# Inputs (2)

cylinderColor Default Value: Modelica.Mechanics.MultiBody.Types.Defaults.JointColor Type: Color Description: Color of cylinders representing the joint axes Default Value: world.defaultSpecularCoefficient Type: SpecularCoefficient Description: Reflection of ambient light (= 0: light is completely absorbed)

# Connectors (2)

frame_a Type: Frame_a Description: Coordinate system a fixed to the component with one cut-force and cut-torque Type: Frame_b Description: Coordinate system b fixed to the component with one cut-force and cut-torque

# Components (3)

world Type: World Description: World coordinate system + gravity field + default animation definition Type: Revolute Description: Revolute joint (1 rotational degree-of-freedom, 2 potential states, optional axis flange) Type: Revolute Description: Revolute joint (1 rotational degree-of-freedom, 2 potential states, optional axis flange)

# Used in Examples (1)

 UniversalConstraint Modelica.Mechanics.MultiBody.Examples.Constraints Body attached by one spring and universal joint or constrained to environment