| 摘要 |
PURPOSE: To effectively prevent wear and tear of a rope by structuring so that when the tension of a rope of the second pulley exceeds the limit value, the first nip position is changed to the second nip position and equipping with a cam having the second control plane which functions in co-operation with the first control plane in accordance with a rotation of a holding plate. CONSTITUTION: A safe descender has a pair of pulleys 12 and 14 housed between parallel flanges 18 and 20. The first pulley 12 is equipped with a circular upper half having a take-up groove 24 for a rope 26 and with the first control plane 28 on the side facing the second pulley 14. When a tension F2 of the rope 26 is higher than the limit value of the device, the safe descender 10 is positioned in the second punch position, and the small supporting plane of a boss 36 forms the first nip position when the limit value of the safe descender 10 does not exceed the tension of the rope 26. When the limit value exceeds the tension F2 of the rope 26, the second control plane 38 forms a large supporting plane at the second nip position and takes charge. Though, the second nip position has a great nip effect, the rope 26 is unlikely to suffer a damage because control planes 28 and 38 of the first and second, have flat surfaces, respectively. |
