The invention relates to a hoisting overspeed slow descent
brake, and discloses an overspeed slow descent
brake of a small crane. The overspeed slow descent
brake detects the running speed of a steel
wire rope in real time through an
infrared steel
wire rope speed sensor, transmits signals through a
signal line and drives a disc-shaped rocker to rotate through a motor, so that a U-shaped sliding block stretches out to clamp the steel
wire rope for
speed reduction. The device is characterized by comprising an overspeed slow descent brake fixing frame, an
infrared steel wire
rope speed sensor, a motor support, a motor, a
signal line, a
crank, a connecting rod, a disc-shaped rocker fixing disc, a fixing bolt, a steel wire
rope sliding groove, a steel wire
rope, a disc-shaped rocker, a U-shaped sliding groove, a U-shaped sliding block and a spring. The
infrared steel wire rope speed sensor is fixedly arranged on one side face of the overspeed slow descent brake fixing frame, a hole is formed in the overspeed slow descent brake fixing frame, and an emitter and a
receiver of the infrared steel wire rope speed sensor both penetrate through a center shaft of the hole of the overspeed slow descent brake fixing frame.