US Patent 7284743 Hoist limiting system

A hoist limiting system (15) comprising a frame (16), a hoist drum (17) supported by the frame and rotatable about a hoist axis (x-x), a hoist driver (19) supported by the frame and configured to rotate the hoist drum in opposite upward (30) and downward (31) directions about the hoist axis, a hoist line (18) in engagement with the hoist drum such that the hoist line winds in the upward or downward direction in response to rotation of the hoist drum, at least one gear (20) mechanically coupling the hoist driver and hoist drum and configured to rotate about a gear axis (x-x), the gear having a face (21) that rotates about the gear axis in a upward or downward direction in response to rotation of the hoist drum, a first proximity limit switch (26) supported by the frame adjacent the rotating face such that the rotating face moves relative to the proximity switch and a second proximity limit switch (28) supported by the frame adjacent the rotating face such that the rotating face moves relative to the second proximity switch, the first and second proximity switches configured to sense the presence or absence of the face and communicating with a controller (29), the first and second proximity switches, the control unit, and the hoist driver configured to prevent the hoist drum from rotating in the upward direction as a function of signals from the first and the second proximity switches and configured and arranged to prevent the hoist drum from rotating in the downward direction as a function of the signals from the first and the second proximity switches.