This mechanism is applied for hand powered lifting apparatus.
When there is a pulling force in blue cable, the yellow rod compresses brown leaf spring and the grey frame can move up down.
When there is no pulling force in blue cable or the cable is broken, the brown spring via yellow rod and green levers pushes two pink pawls into contact with two stationary racks thus the frame is kept immobile.
The moving down is a jerk proccess, pulling force in cable is only big enough to prevent the pawls from contact with the racks.
The video shows how the frame goes up, stops, goes down, stops, goes up again and stops when the cable is broken.
Leaf spring can be replaced with helical cylindrical one.