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

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.

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.