This worksheet allows the kinematic synthesis of a four-bar linkage with constant transmission ratio, defined as the velocity ratio between the two links adjacent to the frame. The cubic of stationary curvature of the relative motion between the two links degenerates into a circle and a line. Point A is chosen on the circle (the one with green color) and point B is the center of curvature of the trajectory of A for the relative motion considered. B is chosen by means of the second Euler-Savary equation. The inflection circle is the one in red. Please note that by virtue of the Freudenstein theorem, the coupler AB is always perpendicular to the collineation axis.
You can set the transmission ratio by moving the slider "a". The position of point A on the cubic is varied by means of the slider "psi".
The frame link length A0B0 has length equal to one.