The coordinate system is defined with x as the axial direction. The y-axis (in green) points up to the middle of the gap before the first ball and the angle ψ is positive around the x-axis or clockwise in the diagram on the right (looking in the direction of the x-axis). The angle starts with zero on the y-axis; the start angle of the ball screw can be changed under settings. Moments are positive if acting around the corresponding axis.
The load is acting on the inner ring, so a positive load in y-direction leads to a loading of the rolling elements on the top.