Two links straighten to move a red slider. As they approach alignment, a change in link angle produces less slider travel. Change link lengths and opening angles to see the difference.
You can also size links a and b from required travel. Set angular limits and the length ratio, then apply the result to check the motion.
At 1×, 15 cycles/min takes 4 seconds per open–close cycle. Playback scale changes elapsed time only, not the motion relationship. Drawing scale stays fixed during playback.
Change blue values → use the button to return to the drawing
Travel alone does not determine link lengths. Also set the angular limits and the ratio between the two links. Travel s is measured from the open position to the closed position.
Lengths are pivot-centre distances. After rounding to available sizes, check the travel again in dimension mode.
Travel is zero at the open position; x in the drawing is distance from fixed point O. Compare blue link angle with red slider position. Slider travel becomes small near alignment. This model does not pass through alignment or model over-centre locking.
O is fixed; B = (a cos θ, a sin θ), C = (a cos θ + √(b² − a² sin² θ), 0). A prescribed cosine motion varies θ between its limits; one cycle is open–close–open. Velocity is the derivative of this position. A minimum angle of 0.2° avoids the dead point. Clamping force, holding, locking, friction, strength and the actuator are not modelled.
