Systems and Methods for Controlling Rotation and Twist of a Tether

Abstract

A system may include a tether, a slip ring, a tether gimbal assembly, a drive mechanism, a control system. The tether may include a distal tether end coupled to an aerial vehicle, a proximate tether end, and at least one insulated electrical conductor coupled to the aerial vehicle. The slip ring may include a fixed portion and a rotatable portion, where the rotatable portion is coupled to the tether. The tether gimbal assembly may be rotatable about at least one axis and is coupled to the fixed portion of the slip ring. The drive mechanism may be coupled to the slip ring and configured to rotate the rotatable portion of the slip ring. And the control system may be configured to operate the drive mechanism to control twist in the tether.

What is claimed is: 
     
         1 . A system comprising:
 a tether comprising:
 a distal tether end coupled to an aerial vehicle; 
 a proximate tether end; and 
 at least one insulated electrical conductor coupled to the aerial vehicle, wherein the tether has an amount of twist between the distal tether end and the proximate tether end; 
   a tether gimbal assembly, wherein the tether gimbal assembly is coupled to the tether and is rotatable about at least a horizontal axis or an azimuth axis;   a drive mechanism coupled to the tether at the proximate tether end, wherein the drive mechanism rotates the tether about a long axis of the tether that extends between the distal tether end and the proximate tether end; and   a control system, wherein the control system operates the drive mechanism to change the amount of twist in the tether.   
     
     
         2 . The system of  claim 1 , wherein the control system operates the drive mechanism in a lag mode. 
     
     
         3 . The system of  claim 1 , wherein the control system operates the drive mechanism in a lead mode. 
     
     
         4 . The system of  claim 1 , wherein the control system operates the drive mechanism by activating and deactivating the drive mechanism. 
     
     
         5 . The system of  claim 1 , wherein the control system operates the drive mechanism by causing the drive mechanism to rotate the tether at a constant rate. 
     
     
         6 . The system of  claim 1 , wherein the control system operates the drive mechanism by causing the drive mechanism to rotate the tether at a variable rate. 
     
     
         7 . A system comprising:
 a tether comprising:
 a distal tether end coupled to an aerial vehicle; 
 a proximate tether end; and 
 at least one insulated electrical conductor coupled to the aerial vehicle; 
   a tether gimbal assembly, wherein the tether gimbal assembly is coupled to the tether and is rotatable about at least a horizontal axis or an azimuth axis; and   a resistive bearing system coupled to the tether gimbal assembly, wherein the resistive bearing system is configured to allow the proximate tether end to rotate when a torque at the proximate tether end exceeds a slip limit, and further configured to inhibit the rotation of the proximate tether end when the torque does not exceed the slip limit.   
     
     
         8 . The system of  claim 7 , wherein the resistive bearing system comprises a brake. 
     
     
         9 . The system of  claim 7 , wherein the resistive bearing system comprises a friction brake. 
     
     
         10 . The system of  claim 7 , wherein the slip limit is based at least in part on a tension of the tether. 
     
     
         11 . The system of  claim 7 , wherein the tether further comprises a torque layer having at least one fiber, wherein the at least one fiber is helically wound around a length of the tether over the at least one insulated conductor, and wherein the at least one fiber is configured to provide a torque to drive the resistive bearing system. 
     
     
         12 . The system of  claim 7  further comprising a slip ring comprising a fixed portion and a rotatable portion, wherein the rotatable portion of the slip ring is coupled to the tether. 
     
     
         13 . The system of  claim 7  further comprising:
 a ground station; and 
 a slip ring comprising a fixed portion and a rotatable portion, wherein the fixed portion of the slip ring is coupled to the ground station. 
 
     
     
         14 . The system of  claim 7  further comprising a slip ring comprising a fixed portion and a rotatable portion, wherein the fixed portion of the slip ring is coupled to the tether gimbal assembly. 
     
     
         15 . A system comprising:
 a tether comprising:
 a distal tether end coupled to an aerial vehicle; 
 a proximate tether end; and 
 at least one insulated electrical conductor coupled to the aerial vehicle, wherein the tether has an amount of twist between the distal tether end and the proximate tether end; 
   a tether gimbal assembly, wherein the tether gimbal assembly is coupled to the tether and is rotatable about at least a horizontal axis or an azimuth axis; and   a resistive bearing system coupled to the tether gimbal assembly, wherein the resistive bearing system is configured to allow the proximate tether end to rotate and to provide a resistance to the rotational torque of the tether so as to maintain the amount of twist in the tether within a determined range of values.   
     
     
         16 . The system of  claim 15 , wherein the resistive bearing system comprises a brake. 
     
     
         17 . The system of  claim 15 , wherein the resistive bearing system comprises a friction brake. 
     
     
         18 . The system of  claim 15  further comprising a slip ring comprising a fixed portion and a rotatable portion, wherein the rotatable portion of the slip ring is coupled to the tether. 
     
     
         19 . The system of  claim 15  further comprising:
 a ground station; and 
 a slip ring comprising a fixed portion and a rotatable portion, wherein the fixed portion of the slip ring is coupled to the ground station. 
 
     
     
         20 . The system of  claim 15  further comprising a slip ring comprising a fixed portion and a rotatable portion, wherein the fixed portion of the slip ring is coupled to the tether gimbal assembly.