Safety break for an overhead door

An arrangement for monitoring a torsion spring in an overhead door for counterbalancing at least one panel in said overhead door to prevent said overhead door from accidentally slamming shut or dropping too rapidly, comprising:

• a blocker, a torque transmitter, a catcher, and a sensor and release assembly for sensing torsion in the spring;
• said torque transmitter being subject to a force exerted by the spring as long as the spring is intact, said blocker rotating around an axis along with said torque transmitter and being mechanically coupled to a detented grabber as said overhead door opens and closes;
• said blocker blocking rotation of said torque transmitter and thereby motion of the overhead door depending on the catcher, said catcher being shiftable out of an inactive position disengaged from the grabber and into an active position, said catcher engaging said grabber in said active position;
• said torsion being absent when said spring breaks, said catcher being shifted out of said inactive position and into said active position when said sensor and release assembly senses absence of said torsion and said catcher engages said grabber of said blocker to block the rotation of said torque transmitter;
• said blocker being at least part of a drum;
• a cable windable about said drum and having an end connected to said overhead door, the torsion in said spring acting through said sensor and release assembly for maintaining the catcher in the inactive position such that when said sensor and release assembly senses that the spring has broken, said sensor and release assembly allowing the catcher to be shifted outward from the inactive position into the active position thereby engaging the grabber of the blocker and preventing rotation of the torque transmitter on which the unbroken spring acts.