Tether management system and method
A tether management system is disclosed. The tether management system includes a spool, a tension sensor, a controller and a moveable pulley. The spool is rotatable to reel in and reel out a tether. The tension sensor measures a tension of the tether. The controller receives a desired tension of the tether and controls the rotation of the spool to reel in and reel out the tether based on a difference between a measured tension from the tension sensor and the desired tension of the tether. The moveable pulley is disposed to engage tether between the spool and the tension sensor. The moveable pulley being able to be biased and moveable along a linear path to adjust a tension of the tether when the tension of the tether deviates from the desired tension. A method for managing tether is also disclosed.
1. A tether management system comprising:
a spool rotatable to reel in and reel out a tether;
a tension pulley engaging the tether;
a tension sensor coupled to the tension pulley for measuring a tension of the tether;
a controller for receiving a desired tension of the tether and for controlling the rotation of the spool to reel in and reel out the tether based on a difference between a measured tension from the tension sensor and the desired tension of the tether;
a moveable pulley that does not directly actuate the tension sensor and is disposed to engage tether between the spool and the tension pulley;
an elongated compression spring for biasing the moveable pulley to be moveable along a linear path to adjust a tension of the tether when the tension of the tether deviates from the desired tension;
a first rod over which the elongated compression spring is sleeved;
a second rod at least substantially parallel to the first rod;
a pulley support for supporting the moveable pulley, the pulley support including two bushings through which the first rod and the second rod penetrate to allow the pulley support to be slidable thereon;
a first end block at a first end of the first rod and the second rod; and
a second end block at a second end of the first rod and the second rod;
wherein the elongated compression spring has a free length that is at least substantially equal to a length of the first rod, and, when biased, has a force of about twice the tension of the tether over a range of operating tension of the tether.
2. The tether management system according to claim 1 , further comprising a limit stop disposed adjacent an intermediate position between the first end block and the second end block to limit movement of the pulley support to be along the first rod and the second rod between the second end block and the limit stop.
3. The tether management system according to claim 1 , wherein the thickness of the spool is in the range of 1-10 times the thickness of the tether.
4. The tether management system according to claim 1 , further comprising a housing having a base, a roof opposite the base and a sidewall between the base and the roof, and wherein the spool is disposed such that a radial plane thereof is at least substantially parallel to the base of the housing.
5. The tether management system according to claim 4 , further comprising:
a fixed pulley disposed to engage tether between the moveable pulley and the tension pulley;
wherein the tension pulley guides the tether along an exit section of a path of the tether extending through the roof of the housing.
6. The tether management system according to claim 5 , wherein the exit section is transverse to the linear path of the moveable pulley.
7. The tether management system according to claim 5 , further comprising:
a bracket to which the tension pulley and the tension sensor are mounted; and
a fairlead mounted to the bracket through which the tether exits the housing, the fairlead including at least one roller that is able to urge the tether against the tension pulley.
8. The tether management system according to claim 1 , wherein the controller is adapted to determine a speed for rotating the spool based on a difference between the measured tension of the tether and the desired tension.
9. The tether management system according to claim 8 , wherein the controller is adapted to further limit the speed for rotating the spool to a cap value corresponding to a length of tether left on the spool when less than a predetermined length of tether is left on the spool.
10. The tether management system according to claim 9 , further comprising a sensor for determining if an end of spool is near, and wherein the controller is adapted to set the speed to zero when the sensor indicates so.
11. The tether management system according to claim 1 , further comprising a guard disposed adjacent the spool to prevent tether slippage.