Bulk material is conveyed over a slat conveyor, and the material is leveled with overhead rollers while being transported in the conveyor to maintain an even material height. Most of these "levelers" operate at a surface speed that is much faster than the speed of the conveyor. However, one particular overhead roll serves to compress the material slightly and feed a machine downstream, and it operates with a surface speed close to the conveyor speed.
This particular roller operates at a constant speed, but the conveyor does not. As such, there are times when the roller has a faster surface speed than the conveyor, but other times when the roller operates more slowly.
Is there a way to calculate the effect of these external devices on the force or energy required to operate the conveyor? I am particularly worried about this last roller, since it seems to cause the most resistance to motion. I have been unable to find even empirical information on the effect of these rollers in standard chain pull calculation guides.