Joint - Local Axes

Form:  Joint Local Axis, Joint Advanced Axis

By default, the joint local 1-2-3 coordinate system is identical to the global X-Y-Z coordinate system. However, it may be necessary to use different local coordinate systems at some or all joints in the following cases: skewed restraints (supports) are present; constraints are used to impose rotational symmetry; constraints are used to impose symmetry about a plane that is not parallel to a global coordinate plane; the principal axes for the joint mass (translational or rotational) are not aligned with the global axes; and joint displacement and force output is desired in another coordinate system.

Joint local coordinate systems need only be defined for the affected joints. The global system is used for all joints for which no local coordinate system is explicitly specified. Advanced methods are available to define a joint local coordinate system. These may be used separately or together. Local coordinate axes may be defined to be parallel to arbitrary coordinate directions in an arbitrary coordinate system or to vectors between pairs of joints. In addition, the joint local coordinate system may be specified by a set of three joint coordinate angles.

  1. Select one or more joints to be assigned the same local axes. Other types of objects may be selected because they will not be affected by this assignment.

  2. Click the Advanced > Assign > Joints > Local Axes command to access the Joint Local Axis form.

  3. Type in a value for rotation angles about the Z, Y’ and X” axes, in degrees (Y’ and X” are used as axes names instead of Y and X to emphasize that the local X and Y axes will change after an angle about Z has been specified).

  4. Check the Use default (Global) check box if the Global definition is to be used for the local axes.

  5. If appropriate, check the Advanced Axes check box and click the Advanced button to access the Joint Advanced Axes form. Use the Joint Advanced Axis form to refine the specification of the local axes for the selected object(s).

EXAMPLE:

 

 

 

See Also

Display- Show Miscellaneous Assigns - Joints