Disk 1 rotates about fixed axis A and has pin a and circular lug b. Lever 2 has pin c and is in its extreme position (as shown) as long as lug b slides along pin c. At this time, pin a bends flat spring 3. When pin c drops off the end of lug b, spring 3 turns lever 2 to its other extreme position. After this, pin a engages the lower branch of spring 3 and returns lever 2 to its initial position.
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