Link 3 has projections a and slot b which slides along fixed block C. The motion of link 3 is due to the action of spring 6. Slider 4 of linkage ABD moves in guide 2 and has lugs d. Link 3 is stopped when a lug d engages a projection a. When lever 1 is turned counterclockwise, the upper projections a of link 3 are engaged. The lower projections are engaged when slider 4 is pulled upward by spring 5. Guide 2 has a certain degree of freedom about fixed axis D. This avoids impacts in the engagements of projections a and lugs d.
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