Methods and systems for damping oscillations of a payload

1. A system comprising:

a winch system for an aerial vehicle, wherein the winch system comprises: (a) a tether disposed on a spool, (b) a motor that is operable to apply torque to the tether via the tether, and (c) a payload coupling apparatus coupled to a leading end of the tether and structured to mechanically couple a payload to the tether;

at least one sensor arranged to generate sensor data indicative of oscillations of the payload coupling apparatus when the tether is at least partially unwound; and

a control system operable to:

while the aerial vehicle is in a hover flight mode, switch to operation in a tether retraction mode; and

while operating in the tether retraction mode:

use the generated sensor data as a basis for detecting oscillation of the payload coupling apparatus; and

perform a damping routine to dampen oscillations of the payload coupling apparatus, wherein the damping routine comprises responding to detection of payload oscillation exceeding a threshold by: (a) while the aerial vehicle is in a position-hold mode, causing the aerial vehicle to reduce an extent of flight stabilization along at least one of the three dimensions, or (b) causing the aerial vehicle to switch from the hover flight mode to a forward flight mode in which movement of the aerial vehicle results in drag on the payload coupling apparatus.

2. The system of claim 1 , wherein the at least one sensor comprises one or more of the following sensors: (i) a current sensor arranged to generate data representative of electric current characteristics of the motor, (ii) an image capture device arranged to generate image data indicative of movement of the payload coupling apparatus relative to the aerial vehicle, (iii) an inertial measurement unit arranged to generate movement data indicative of movement of the payload coupling apparatus relative to the aerial vehicle, (iv) an encoder arranged to generate position data representative of an unwound length of the tether, and (v) a tension sensor arranged to generate tension data representative of tension of the tether.

3. The system of claim 1 , wherein the damping routine comprises causing the aerial vehicle to switch from the hover flight mode to the forward flight mode in which movement of the aerial vehicle results in drag on the payload coupling apparatus, wherein the drag dampens the oscillations of the payload coupling apparatus.

4. The system of claim 3 , further comprising at least one sensor arranged to generate sensor data indicative of oscillations of the payload coupling apparatus when the tether is at least partially unwound, and wherein the control system is further operable to:

pause retraction of the tether;

based at least in part on the sensor data, detect that oscillations of the payload coupling apparatus have been sufficiently dampened by the drag; and

in response to detecting that oscillations of the payload coupling apparatus have been sufficiently dampened by the drag, resume retraction of the tether to lift the payload coupling apparatus to the aerial vehicle.

5. The system of claim 3 , wherein the control system is further operable to:

pause retraction of the tether;

upon causing the aerial vehicle to switch from the hover flight mode to the forward flight mode, initiate a timer that is arranged to expire after a particular duration; and

detect expiration of the timer after the particular duration, and responsively resume retraction of the tether to lift the payload coupling apparatus to the aerial vehicle.

6. The system of claim 1 ,

wherein the aerial vehicle is operable in the position-hold to substantially maintain a physical position during hover flight by engaging in flight stabilization along three dimensions in physical space, and

wherein the damping routine comprises, while the aerial vehicle is in the position-hold mode, causing the aerial vehicle to reduce the extent of flight stabilization along at least one of the three dimensions, thereby resulting in damping of the oscillations due to energy dissipation during movement of the aerial vehicle along the at least one dimension.

7. The system of claim 6 , wherein the at least one sensor is arranged to generate sensor data indicative of oscillations of the payload coupling apparatus when the tether is at least partially unwound, wherein the control system is further operable to:

based at least in part on the sensor data, detect the oscillations of the payload coupling apparatus; and

based at least on the detected oscillations, determine a target extent of flight stabilization along the at least one dimension, and

wherein causing the aerial vehicle to reduce the extent of flight stabilization along the at least one dimension comprises causing the aerial vehicle to reduce the extent of flight stabilization along the at least one dimension to the determined target extent.

8. The system of claim 6 , wherein the at least one sensor is arranged to generate sensor data indicative of oscillations of the payload coupling apparatus when the tether is at least partially unwound, and wherein the control system is further operable to:

based at least in part on the sensor data, detect that oscillations of the payload coupling apparatus have been sufficiently dampened following reduction in the extent of flight stabilization along the at least one dimension; and

in response to detecting that oscillations of the payload coupling apparatus have been sufficiently dampened, cause the aerial vehicle to increase the extent of flight stabilization along the at least one dimension.

9. The system of claim 6 , wherein the control system is further operable to:

upon causing the aerial vehicle to reduce the extent of flight stabilization along the at least one dimension, initiate a timer that is arranged to expire after a particular duration; and

detect expiration of the timer after the particular duration, and responsively cause the aerial vehicle to increase the extent of flight stabilization along the at least one dimension.

10. The system of claim 6 , further comprising at least one sensor arranged to generate sensor data indicative of oscillations of the payload coupling apparatus when the tether is at least partially unwound, and wherein the control system is further operable to:

pause retraction of the tether;

based at least in part on the sensor data, detect that oscillations of the payload coupling apparatus have been sufficiently dampened following reduction in the extent of flight stabilization along the at least one dimension; and

in response to detecting that oscillations of the payload coupling apparatus have been dampened to at least a predetermined extent, resume retraction of the tether to lift the payload coupling apparatus to the aerial vehicle.

11. The system of claim 6 , wherein the control system is further operable to:

pause retraction of the tether;

upon causing the aerial vehicle to reduce the extent of flight stabilization along the at least one dimension, initiate a timer that is arranged to expire after a particular duration; and

detect expiration of the timer after the particular duration, and responsively resume retraction of the tether to lift the payload coupling apparatus to the aerial vehicle.

12. The system of claim 1 ,

wherein the motor being operable to apply torque to the tether comprises the motor being operable in both a first mode and a second mode to apply torque to the tether in a winding direction and an unwinding direction, respectively,

wherein operation in the tether retraction mode comprises at least operating the motor in the first mode to retract the tether at a retraction rate, and

wherein the damping routine comprises, while operating in the tether retraction mode, operating the motor to vary the retraction rate based on the detected oscillation.

13. A system comprising:

a winch system for an aerial vehicle, wherein the winch system comprises: (a) a tether disposed on a spool and (b) a motor that is operable to apply torque to the tether;

at least one sensor arranged to generate sensor data indicative of oscillations of the payload; and

a control system operable to:

while the aerial vehicle is in a hover flight mode;

determine, based at least in part on the generated sensor data, that the detected oscillations exceed a threshold;

responsive to determining that the detected oscillations exceed the threshold, cause the aerial vehicle to switch from the hover flight mode to a forward flight mode in which movement of the aerial vehicle results in drag on a payload that is coupled to the tether, wherein the drag dampens oscillations of the payload when the tether is at least partially unwound.

14. The system of claim 13 , wherein the payload is a payload coupling apparatus coupled to a leading end of the tether and structured to mechanically couple another payload.

15. The system of claim 13 , wherein the at least one sensor comprises one or more of the following sensors: (i) a current sensor arranged to generate data representative of electric current characteristics of the motor, (ii) an image capture device arranged to generate image data indicative of movement of the payload relative to the aerial vehicle, (iii) an inertial measurement unit arranged to generate movement data indicative of movement of the relative to the aerial vehicle, (iv) an encoder arranged to generate position data representative of an unwound length of the tether, and (v) a tension sensor arranged to generate tension data representative of tension of the tether.

16. The system of claim 13 , further comprising at least one sensor arranged to generate sensor data indicative of oscillations of the payload, wherein the motor being operable to apply torque to the tether comprises the motor being operable in both a first mode and a second mode to apply torque to the tether in a winding direction and an unwinding direction, respectively, and wherein the control system is further operable to:

retract the tether by operating the motor in the first mode;

based at least in part on the sensor data, detect that oscillations of the payload exceed a threshold;

while the detected oscillations exceed the threshold, operate the motor to pause retraction of the tether;

based at least in part on the sensor data, detect that oscillations of the payload have been sufficiently dampened by the drag; and

in response to detecting that oscillations of the payload have been sufficiently dampened by the drag, operate the motor in the first mode to resume retraction of the tether.

17. The system of claim 13 , wherein the motor being operable to apply torque to the tether comprises the motor being operable in both a first mode and a second mode to apply torque to the tether in a winding direction and an unwinding direction, respectively, and wherein the control system is further operable to:

retract the tether by operating the motor in the first mode;

operate the motor to pause retraction of the tether;

upon causing the aerial vehicle to switch from the hover flight mode to the forward flight mode, initiate a timer that is arranged to expire after a particular duration;

detect expiration of the timer after the particular duration; and

in response to detecting expiration of the timer after the particular duration, operate the motor in the first mode to resume retraction of the tether.

18. The system of claim 13 , wherein the motor being operable to apply torque to the tether comprises the motor being operable in both a first mode and a second mode to apply torque to the tether in a winding direction and an unwinding direction, respectively, and wherein the control system is further operable to:

deploy the tether by operating the motor in the second mode;

operate the motor to pause deployment of the tether;

upon causing the aerial vehicle to switch from the hover flight mode to the forward flight mode, initiate a timer that is arranged to expire after a particular duration;

detect expiration of the timer after the particular duration; and

in response to detecting expiration of the timer after the particular duration, operate the motor in the second mode to resume deployment of the tether.