Dynamic reduction-ratio hoisting device
A hoisting device including a cable drum, a first motor, a second motor and a gear assembly is provided. The gear assembly includes a first epicyclic and a second epicyclic. The first epicyclic includes a first carrier rotationally connected to the cable drum, a first sun rotationally connected to the first motor, a first annulus, and a first planet in meshing engagement with the first sun and the first annulus. The second epicyclic includes a second carrier rotationally grounded, a second sun rotationally connected to the second motor, a second annulus connected to the first annulus, and a second planet in meshing engagement with the second sun and the second annulus.
1. A hoisting device comprising:
a cable drum;
a first motor;
a second motor; and
a gear assembly comprising a first epicyclic and a second epicyclic,
the first epicyclic comprising:
a first carrier rotationally connected to the cable drum;
a first sun rotationally connected to the first motor;
a first annulus;
a first planet in meshing engagement with the first sun and the first annulus;
the second epicyclic comprising:
a second carrier rotationally grounded;
a second sun rotationally connected to the second motor;
a second annulus connected to the first annulus; and
a second planet in meshing engagement with the second sun and the second annulus;
wherein the first motor and the second motor are operable only as motors in the same or opposite directions;
wherein the hoisting device is a drawworks.
2. A hoisting device according to claim 1 wherein the first annulus and the second annulus are integral and form a common annulus.
3. A hoisting device according to claim 2 wherein the first annulus and the second annulus are rotationally connected.
4. A hoisting device according to claim 3 wherein the first annulus and the second annulus are rotationally connected by a gear train.
5. A hoisting device according to claim 2 wherein a total geometric reduction ratio for each torque path from each of the first motor to the cable drum and the second motor to the cable drum provides for maximum design hook-load with only one of the first motor or the second motor running.
6. A hoisting device according to claim 5 wherein the first epicyclic and second epicyclic are symmetrical.
7. A hoisting device according to claim 6 further comprising a first braking means for preventing rotation of the first sun if the first motor is not running.
8. A hoisting device according to claim 7 further comprising a second braking means for preventing rotation of the second sun if the second motor is not running.
9. A hoisting device according to claim 1 wherein the first epicyclic and the second epicyclic are concentrically arranged.
10. A hoisting device according to claim 9 wherein the second sun is disposed on a hollow shaft and the first sun is disposed on a first motor shaft extending through the hollow shaft.
11. A hoisting device according to claim 10 comprising a gear train rotationally connecting the second sun to the second motor.
12. A hoisting device according to claim 11 wherein the gear train comprises a proximal gear fixed to the hollow shaft and a distal gear fixed to a second motor shaft.
13. A hoisting device according to claim 12 wherein the gear assembly further comprises a third epicyclic rotationally connecting the first carrier to the cable drum, wherein the first carrier is in meshing engagement with a third sun of the third epicyclic, the third sun is in meshing engagement with a third planet of the third epicyclic, the third planet is in meshing engagement with a rotationally grounded third annulus of the third epicyclic and connected to a third carrier of the third epicyclic, and the third carrier is in meshing engagement with the cable drum.
14. A hoisting device according to claim 13 wherein the second carrier is fixed to a housing of the hoisting device.