The AX function returns the rotational displacement of marker i about the x-axis of marker j, and accounts for angle wrapping.
Marker j defaults to the global coordinate system if it is not specified. This value is computed as follows: assume that rotations about the other two axes (y- and z-axes) of marker j are zero. Then, AX is the angle between the two y-axes (or the two z-axes). AX is measured in a counter-clockwise sense from the y-axis of marker J to the y-axis of marker I (see the figure below).
Measurement of AX
AX(i[,j])
| i | The marker whose rotations are being sought. |
| j | The marker whose coordinate system is used as a reference to calculate the rotations of marker i. When j is not specified, ADAMS/Solver (FORTRAN) defaults to the global coordinate system. |
Mathematically, AX is calculated as:
Cautions
For large rotations (greater than 10 degrees) about the y-axis or z-axis on Marker j, the AX function becomes increasingly non-physical. Moreover, AX is undefined when both arguments to ATAN2 are zero. This occurs when the z-axis of marker i is orthogonal to the plane defined by the y and z-axis of the j marker.
Tips
If you want to change the AX function so it does not account for angle wrapping, use the MOD function. For example, use the function:
(MOD(AX(2,1) + PI, 2 * PI) - PI
The MOD function achieves the cyclic effect and the +PI and -PI shift the curve accordingly.
-20*AX(43,32)
The value of the function is -20 times the angle between the y axes of Markers 43 and 32. The angle is measured counterclockwise from the y-axis of Marker 32 to the y-axis of Marker 43.