Link 1, rotating about fixed axis A, is connected by turning pair C to slider 3 which slides along slot b of link 2. Link 2 rotates about fixed axis D. Slider 3 can be clamped at various positions in slot a. When crank 1 rotates about axis A, slotted link 2 rotates about axis B so that the average transmission ratio between links 1 and 2 equals i₁₂=ω₁/ω₂=1. Since axis B is parallel to but out of line with axis A, in one revolution of crank 1 at constant angular velocity, slotted link 2 also makes one revolution but at variable angular velocity. The angular velocity of slotted link 2 can be changed by adjusting slider 3 along slot a of crank 1 and clamping the slider.
$986$LG,4L$