Belt-on-belt drives for steeply-sloped portions of long conveyors

1. A conveyor system, at least one portion of the conveyor system traversing a continuous slope sufficiently steep such that tensile forces associated with overcoming the effects of the continuous slope are several times larger per unit length of run than tensile forces per unit length of run due to main frictional resistance of the conveyor system, the conveyor system comprising:

an external belt defining a continuous loop, the continuous loop traversing the entire route of the conveyor system and configured to carry material load to be transported across the entire route;

an external drive having a first torque output;

at least one internal belt positioned inside the continuous loop of said external belt and traversing at least a portion of the continuous slope, an upper side of said at least one internal belt configured to operably engage an underside of said external belt so as to frictionally drive a portion of said external belt;

wherein said at least one internal belt has a tensile capacity sufficient to move at least a mass of the material load that is disposed over said at least one internal belt, and said external belt further has a tensile capacity sufficient to move substantially a mass of the material load that is not disposed over said at least one internal belt; and wherein a longitudinal stiffness of said at least one internal belt is at least as stiff as a longitudinal stiffness of said external belt; and

an internal drive having a second torque output, wherein the first torque output is approximately equal to the torque required to move a total mass of the portion of said external belt not resting on said at least one internal belt and the second torque output is approximately equal to the torque required to move a total mass of the portion of said external belt resting on said at least one internal belt.

2. The conveyor system of claim 1 , wherein the longitudinal stiffness of said at least one internal belt is greater than the longitudinal stiffness of said external belt.

3. The conveyor system of claim 2 , wherein each of said external belt and at least one internal belt comprises a plurality of tension members running the length of the respective belts, and wherein the greater longitudinal stiffness of the at least one internal belt relative to the longitudinal stiffness of the external belt is caused by one or more of,

a. said at least one internal belt having a greater ST rating than said external belt,

b. said tension members of said at least one internal belt being constructed to have a first winding pattern, and said tension members of said external belt being constructed to have a second winding pattern, said first winding pattern producing a greater stiffness in said tension members of said at least one internal belt than a stiffness produced by said second winding pattern of said tension members of said external belt, or

c. said tension members of the external belt comprising a plurality of load-carrying members stranded about a central core, wherein the central core is constructed of a material that is radially compressible and has a lower longitudinal stiffness than the load-carrying members.

4. A conveyor system, at least one portion of the conveyor system traversing a continuous slope sufficiently steep such that tensile forces associated with overcoming the effects of the continuous slope are several times larger per unit length of run than tensile forces per unit length of run due to main frictional resistance of the conveyor system, the conveyor system comprising:

an external belt defining a continuous loop, the continuous loop traversing the entire route of the conveyor system, said external belt being configured to carry a material load to be transported across the entire route;

an external drive configured to at least partially drive said external belt;

at least one internal belt positioned inside the continuous loop of the external belt and traversing at least a portion of the continuous slope, an upper side of the at least one internal belt configured to operatively engage an underside of the external belt so as to frictionally drive a portion of the external belt, wherein the stiffness of the internal belt is at least as stiff as the external belt, wherein said at least one internal belt has a tensile capacity sufficient to move at least a mass of the material load that is disposed over said at least one internal belt, and said external belt further has a tensile capacity sufficient to move substantially a mass of the material load that is not disposed over said at least one internal belt; and

an internal drive configured to drive at least said at least one internal belt.

5. The conveyor system of claim 4 , wherein said at least one internal belt is configured to at least one of transition from a substantially flat configuration to a substantially fully troughed configuration at a tail of said at least one internal belt so as to operatively engage said external belt along an area of engagement defined between said external and at least one internal belt, or transition from the substantially fully troughed configuration to the substantially flat configuration at a head of said at least one internal belt so as to operably disengage from said external belt.

6. The conveyor system of claim 5 , wherein when said at least one internal belt engages with said external belt, said external belt forms into a trough having steeper sides than said troughed configuration of said at least one internal belt, in said area of engagement.

7. The conveyor system of claim 5 , further comprising a plurality of carry idlers disposed beneath one or more of said external belt and said at least one internal belt along a longitudinal length of said respective belts, wherein a spacing between successive carry idlers disposed in the area of engagement is different than a spacing between carry idlers disposed outside the area of engagement.

8. The conveyor system of claim 5 , further comprising a support mechanism that facilitates at least one transition length of engagement or disengagement of the external belt and the at least one internal belt, said support mechanism comprising at least one of air-support panels, slider pads, or small-diameter idlers.

9. The conveyor system of claim 8 , wherein the support mechanism is supported from above such that at least portions of lateral trough walls of said at least one internal belt are in close proximity to at least portions of lateral trough walls of said external belt.

10. The conveyor system of claim 5 , wherein said external belt is flattened to facilitate at least one of engaging and disengaging said at least one internal belt.

11. The conveyor system of claim 10 , further comprising a cover belt disposed above and in operative communication with said external belt, and configured to form an inverted trough to contain a material load on said external belt when said external belt is in a flattened state.

12. The conveyor system of claim 4 , further comprising:

at least a first drive pulley in operative communication with said external belt and configured to drive said external belt;

at least a second drive pulley in operative communication with said internal belt and configured to drive said at least one internal belt; and

a control system configured to control a speed of at least one of said at least first or at least second drive pulleys driving said respective external belt or at least one internal belt to achieve correct progression of each respective belt.

13. The conveyor system of claim 12 , wherein said control system controls said external belt and said at least one internal belt to progress at a substantially similar speed.

14. The conveyor system of claim 4 , further comprising a control system configured to control a torque directed to at least one of a drive pulley of said external belt or a drive pulley of said at least one internal belt to ensure that each respective belt carries a proportionate share of a total tension and that a friction capacity of the interface between said respective belts is not exceeded.

15. The conveyor system of claim 14 , wherein said conveyor system further comprises a belt scale installed near a tail of said external belt and configured to continuously measure a mass of payload passing over said external belt, wherein said control system comprises a load profile component and a drive control component, said load profile component being configured to use measurements taken by said belt scale to calculate a load profile of the entire conveyor system, and wherein said drive control component being configured to use the load profile of the entire conveyor system to proportion load to said respective drive pulleys for said at least one internal belt and for said external belt to ensure that each respective drive pulley is driving to the appropriate extent.

16. The conveyor system of claim 4 , wherein a longitudinal stiffness of said at least one internal belt is greater than a longitudinal stiffness of said external belt.

17. The conveyor system of claim 16 , wherein each of said external belt and at least one internal belt comprises a plurality of tension members running the length of the respective belts, wherein the longitudinal stiffness of said at least one internal belt is greater than the longitudinal stiffness of said external belt, and wherein the greater longitudinal stiffness of said at least one internal belt relative to the longitudinal stiffness of said external belt is achieved by one or more of,

a. said at least one internal belt having a greater ST rating than said external belt;

b. said tension members of said at least one internal belt being constructed to have a first winding pattern, and said tension members of said external belt being constructed to have a second winding pattern, said first winding pattern producing a greater stiffness in said tension members of said at least one internal belt than a stiffness produced by said second winding pattern of said tension members of said external belt, or

c. said tension members of said external belt comprising a plurality of load-carrying members stranded about a central core, wherein the central core is constructed of a material that is radially compressible and has a lower longitudinal stiffness than the load-carrying members.

18. A conveyor system, at least one portion of the conveyor system traversing a continuous slope sufficiently steep such that tensile forces associated with overcoming the effects of the continuous slope are several times larger per unit length of run than tensile forces per unit length of run due to main frictional resistance of the conveyor system, the conveyor system comprising:

an external belt defining a continuous loop, the continuous loop traversing the entire route of the conveyor system and configured to carry material load to be transported across the entire route;

at least one internal belt positioned inside the continuous loop of the external belt and traversing at least a portion of the continuous slope, an upper side of the at least one internal belt configured to operably engage an underside of the external belt so as to frictionally drive a portion of the external belt, wherein a longitudinal stiffness of the internal belt is greater than a longitudinal stiffness of the external belt; and

at least a first drive pulley in operative communication with said external belt and configured to exert an external driveset torque to drive said external belt, said external driveset torque having

a first torque portion sufficient to move a mass of the material load that is not disposed over said at least one internal belt, and

a second torque portion sufficient to move a first share of a mass of the material load that is disposed over said at least one internal belt; and

at least a second drive pulley in operative communication with said internal belt and configured to exert an internal driveset torque to drive said at least one internal belt,

wherein a sum of said internal driveset torque and said second torque portion is approximately equal to an amount of torque required to move a total mass of the material load that is disposed over said at least one internal belt, and

wherein a ratio of said second torque portion to said internal driveset torque is substantially equal to a ratio of the longitudinal stiffness of said external belt to the longitudinal stiffness of said at least one internal belt.

19. The conveyor system of claim 18 , wherein each of said external belt and at least one internal belt comprises a plurality of tension members running the length of the respective belts, and wherein the greater longitudinal stiffness of said at least one internal belt relative to the longitudinal stiffness of said external belt is achieved by one or more of,

a. said at least one internal belt having a greater ST rating than said external belt;

b. said tension members of said at least one internal belt being constructed to have a first winding pattern, and said tension members of said external belt being constructed to have a second winding pattern, said first winding pattern producing a greater stiffness in said tension members of said at least one internal belt than a stiffness produced by said second winding pattern of said tension members of said external belt, or

c. said tension members of said external belt comprising a plurality of load-carrying members stranded about a central core, wherein the central core is constructed of a material that is radially compressible and has a lower longitudinal stiffness than the load-carrying members.