Hoist cable load sensor
A load sensing device for a rescue hoist includes a load pin mounted coaxially with a traction sheave. A cable extends from a cable drum and over the traction sheave before exiting the rescue hoist. The traction sheave is rotatably driven about a traction sheave axis to maintain a back tension on the portion of the cable extending between the cable drum and the traction sheave. When the cable is loaded, strain gauges in the load pin sense a strain on the load pin caused by the load, and the strain information is communicated to a load calculator. Entry angle information is also determined and communicated to the load calculator. The load calculator determines the load on the cable based on the strain information and the entry angle information.
1. A load sensing device for an aircraft-mounted rescue hoist, the load sensing device comprising:
a load pin extending into a first side of a traction sheave and disposed coaxially with the traction sheave on a traction sheave axis, the traction sheave configured to maintain a cable tension on a portion of a cable extending between the traction sheave and a cable drum;
a drive arm connected to a second side of the traction sheave and disposed coaxially with the traction sheave, the drive arm configured to drive rotation of the traction sheave about the traction sheave axis and relative to the load pin to maintain the cable tension on the portion of the cable extending between the cable drum and the traction sheave; and
a load calculator communicatively connected to the load pin, the load calculator configured to receive a sensed strain from the load pin, to determine an entry angle of the cable to the traction sheave, and to determine a cable load based on the sensed strain and the entry angle;
wherein the cable is wrapped on the cable drum such that the cable is stacked in a plurality of cable wrap layers extending radially relative to a cable drum axis of rotation; and
wherein the entry angle is based on which one of the plurality of cable wrap layers is a radially outermost one of the plurality of cable wrap layers.
2. The device of claim 1 , wherein the drive arm is configured both to underdrive the traction sheave relative to the cable drum and to overdrive the traction sheave relative to the cable drum.
3. The device of claim 1 , further comprising:
a bearing supporting the traction sheave on the load pin such that the traction sheave is rotatable relative to the load pin.
4. The device of claim 3 , wherein:
an inner race of the bearing is disposed about and supported on the load pin; and
an outer race of the bearing is attached to the traction sheave.
5. The device of claim 1 , wherein the load pin is cantilevered and includes a distal end disposed within and supporting the traction sheave.
6. The device of claim 5 , wherein the load pin further comprises:
a body extending into the traction sheave, the body including the distal end and a bore extending through the body;
an circumferential groove extending into an outer surface of the body; and
a strain gauge disposed within the bore and mounted relative to the circumferential groove.
7. The device of claim 6 , wherein the load pin further comprises a mounting flange extending from the body, the mounting flange disposed on an opposite side of the circumferential groove from the distal end.
8. The device of claim 1 , wherein the load calculator comprises:
a processor; and
a memory encoded with instructions that, when executed by the processor, cause the processor to determine the cable load based on an intersection of a first variable and a second variable in a look-up table.
9. The device of claim 8 , wherein:
the first variable is the entry angle; and
the second variable is the sensed strain.
10. A rescue hoist comprising:
a cable drum rotatable about a cable drum axis, wherein the cable drum is driven to rotate the cable drum about the cable drum axis to spool and unspool a cable from the cable drum, and wherein the cable is stacked on the cable drum in a plurality of cable wrap layers extending radially relative to the cable drum axis;
a stationary frame supporting the cable drum;
a traction sheave configured to maintain a back tension on a portion of the cable extending between the cable drum and the traction sheave, the traction sheave rotatable about a traction sheave axis;
a load pin extending into a first side of the traction sheave and disposed coaxially with the traction sheave, the load pin comprising:
a body including a distal end and a bore extending through the body, the distal end extending at least partially into the traction sheave; and
a strain gauge mounted within the bore;
a drive arm disposed coaxially with the traction sheave and connected to a second side of the traction sheave, the drive arm configured to drive the traction sheave about the traction sheave axis to thereby maintain the back tension; and
a load calculator connected to the load pin and configured to receive a sensed strain from the load pin, to determine an entry angle of the cable to the traction sheave from the cable drum, and to determine a cable load based on the sensed strain and the entry angle;
wherein the entry angle is based on which one of the plurality of cable wrap layers is a radially outermost cable wrap layer of the plurality of cable wrap layers.
11. The rescue hoist of claim 10 , wherein the drive arm is configured both to underdrive the traction sheave relative to the cable drum and to overdrive the traction sheave relative to the cable drum.
12. The rescue hoist of claim 11 , wherein the drive arm is configured to rotate the traction sheave concurrently with a cable drum rotation.
13. The rescue hoist of claim 10 , further comprising:
a bearing supporting the traction sheave on the load pin such that the traction sheave is rotatable relative to the load pin.
14. The rescue hoist of claim 13 , wherein the bearing comprises:
an inner race disposed about and supported on the load pin; and
an outer race attached to the traction sheave;
wherein the load pin supports the traction sheave through the bearing.
15. The rescue hoist of claim 10 wherein the load calculator comprises:
a processor; and
a memory encoded with instructions that, when executed by the processor, cause the processor to determine the cable load based on an intersection of a first variable and a second variable in a look-up table;
wherein the first variable is the entry angle and the second variable is the sensed strain.
16. The rescue hoist of claim 10 , wherein the load calculator is further configured to determine which cable wrap layer of the plurality of cable wrap layers is the radially outermost cable wrap layer based on a length of cable deployed from the cable drum.
17. The device of claim 1 , wherein the load calculator is configured to determine which one of the plurality of cable wrap layers is the radially outermost one of the plurality of cable wrap layers based on a length of the cable deployed from the cable drum.