This segment is best explained by considering the X and Y motion components of a Point that is at the end of a rotating Part or Crank. When the Crank rotates with constant angular velocity, the horizontal* motion of a Point at the end of the Crank is 'SimpleHarmonicMotion' [ a Sine function] When you apply the 'Y–Inverse Sinusoid' segment to a Crank, the Point can be made to move with a constant linear horizontal* velocity for a portion of the crank's rotation. * Actually, the motion of a Point on a Crank projected on to any line is SimpleHarmonicMotion. 

If EP > SP, then the ConstantVelocity motion is from left to right, not right to left 
Segment Parameters.
The maximum range of the Rocker = ± Radius of the Rocker. The Radius of the Rocker specifies the maximum amplitude of the SimpleHarmonicMotion.
Start Position must be within the maximum range as specified by the 'Rocker Radius' parameter ±100% × Rocker [practically less than this] Specifies the motion value, in linear units, that the tip of the part is at when it starts to move at a ConstantVelocity.
End Position must be within the maximum range as specified by the 'Rocker Radius' parameter ±100% × Rocker [practically less than this] Specifies the motion value, in linear units, that the tip of the part is at when it ends tits move at a ConstantVelocity. 

If SP > EP, then the ConstantVelocity of the Point is from Right to Left. If EP > SP, then the ConstantVelocity of the Point is from Left to Right. The example motion, with two segments. Segment 1:
With these Parameters:
Segment 2:
This means the Crank rotates
NOTE: The motion is most typically applied to rotating Parts  that is Cranks or Rockers. However, it can be used to control the motion of any Part for any reason  just like any other motion. 

† Why 60º? It is the angle of a triangle with the Hypotenuse of 100mm (Radius of Rocker) and an Adjacent of 50mm (Start Position). ‡ Why 120º? It is the supplementary and obtuse angle of a triangle with the Hypotenuse of 100mm (Radius of Rocker) and an Adjacent of 50mm (End Position).


Crank in MechDesigner.
Do not connect a wire from the Motion FB to the Motion Dimension FB.
This Part can be a 'Crank' for a Scotch Yoke Mechanism. 

At 0º of the Master Machine Angle, the output of the Y–Inverse Sinusoid is 60º. Hence, the 'Crank' moves to 60º when we 'Home' the Master Machine Angle. Between 0 and 90 of the MMA:
Between 90 and 360 of the MMA


This is a schematic of a 'ScotchYoke' mechanism. The End of the Crank has a Pin which engages in a slot. The Slot is vertical in this case, and rigidly attached to a slider that can slide in the horizontal direction. As the Crank rotates, the Slider moves right to left and then left to right. While the crank is between 60º and 120º, the Slider moves to the Left with a ConstantVelocity. 