Positioning assembly for a wind turbine rotor blade lifting device

1. A lift system for lifting or lowering a rotor blade to and from a hub mounted atop a tower of a wind turbine, the lift system comprising:

a lifting device comprising at least one cradle, the at least one cradle comprising a profile that corresponds to at least one of the exterior surfaces of the rotor blade so as to support at least a portion of the rotor blade; and

a positioning assembly comprising at least one distance sensor mounted to the hub, a positioning target secured to the lifting device via one or more magnets, and at least one visual sensor mounted to the lifting device, the distance sensor configured to identify a distance from the hub to the lifting device, the at least one visual sensor configured to identify a position of the rotor blade in the cradle.

2. The lift system of claim 1 , wherein the at least one distance sensor comprises an emitter and a receiver.

3. The lift system of claim 2 , wherein the emitter comprises an infrared light and the receiver comprises a camera.

4. The lift system of claim 1 , wherein the at least one distance sensor is mounted to a pitch bearing of the wind turbine.

5. The lift system of claim 3 , wherein the emitter is configured to emit signals to the positioning target, the receiver is configured to receive signals from the positioning target to identify the distance from the hub to the lifting device.

6. The lift system of claim 1 , wherein the at least one distance sensor comprises Wi-Fi capabilities.

7. The lift system of claim 1 , wherein the at least one visual sensor comprises, at least, a first set of sensors comprising a first visual sensor and a second visual sensor.

8. The lift system of claim 7 , wherein the first and second visual sensors comprise cameras.

9. The lift system of claim 7 , wherein the lifting device further comprises a root cradle for supporting the root of the rotor blade and a tip cradle for supporting the tip of the rotor blade.

10. The lift system of claim 9 , wherein the first and second visual sensors are mounted to the root cradle.

11. The lift system of claim 10 , wherein the first visual sensor is mounted to a lower support member of the root cradle so as to view a span-wise direction of the rotor blade and the second visual sensor is mounted to an opposing upper support member of the root cradle so as to view a chord-wise direction of the rotor blade.

12. The lift system of claim 7 , wherein the at least one visual sensor comprises, at least, a second set of visual sensors mounted to the tip cradle.

13. The lift system of claim 9 , wherein the lifting device further comprises a structural frame body for connecting and supporting the root cradle and the tip cradle.

14. The lift system of claim 1 , further comprising one or more safety features configured to restrict movement of the rotor blade.

15. A method for lowering a rotor blade from a hub mounted atop a tower of a wind turbine, the method comprising:

mounting at least one distance sensor of a positioning assembly to the hub;

lifting, via a crane, a lifting device from a ground location to the hub, the lifting device having root and tip cradles for supporting the rotor blade, at least one visual sensor mounted thereto, and a positioning target secured to the lifting device via one or more magnets;

positioning the lifting device with respect to the hub via the distance sensor;

mounting the lifting device to the rotor blade;

positioning the rotor blade into the root and tip cradles of the lifting device using the at least one visual sensor;

detaching the rotor blade from the hub; and

lowering, via the crane, the rotor blade from the hub to the ground location,

wherein the root and tip cradles each have a profile that corresponds to respective root and tip exterior surfaces of the rotor blade.

16. The method of claim 15 , wherein mounting the at least one distance sensor of the positioning assembly to the hub further comprises mounting the at least one distance sensor to a pitch bearing of the hub.

17. The method of claim 15 , wherein positioning the lifting device with respect to the hub via the distance sensor further comprises:

securing a positioning target to the lifting device;

emitting, via an emitter of the at least one distance sensor, one or more signals to the positioning target;

receiving, via a receiver of the at least one distance sensor, the one or more signals from the positioning target to identify a distance between the lifting device and the hub.

18. The method of claim 15 , wherein the at least one visual sensor comprises, at least, a first set of sensors comprising a first visual sensor and a second visual sensor.

19. The method of claim 18 , further comprising:

mounting the first visual sensor to the root cradle to a lower support member of the root cradle so as to view a span-wise direction of the rotor blade; and,

mounting the second visual sensor to an opposing upper support member of the root cradle so as to view a chord-wise direction of the rotor blade.

20. A lift system for lifting or lowering a rotor blade to and from a hub mounted atop a tower of a wind turbine, the lift system comprising:

a lifting device comprising a root cradle for supporting the root of the rotor blade and a tip cradle for supporting the tip of the rotor blade; and

a positioning assembly comprising at least one distance sensor mounted to the hub and at least one visual sensor mounted to the lifting device, the distance sensor configured to identify a distance from the hub to the lifting device, the at least one visual sensor configured to identify a position of the rotor blade in the cradle, the visual sensor comprising at least, a first set of sensors comprising a first visual sensor and a second visual sensor, the first visual sensor being mounted to a lower support member of the root cradle so as to view a span-wise direction of the rotor blade and the second visual sensor being mounted to an opposing upper support member of the root cradle so as to view a chord-wise direction of the rotor blade.