Positive drive helical conveyor system

A conveyor system comprising

• an endless flat belt having a plurality of links connected together and adapted for alternate collapse and expansion along at least one edge of said belt to permit passage of the belt around lateral curves, said belt having protrusions spaced along at least one edge thereof, each of said protrusions having a side surface and an end surface,
• means to support said belt for passage through an endless path including a helical portion extending through a plurality of vertically spaced circular loops with the belt curved laterally in each of said loops, with said protrusions on the radially inner edge thereof, a planar approach portion leading tangentially into the first loop at one end of said helical portion and a planar exit portion leading tangentially away from the last loop at the other end of said helical portion, guide means directing said belt into said planar approach portion,
• primary drive means comprising a cylindrical cage rotatable about a vertical axis and having a plurality of vertical driving bars spaced circumferentially around the cage, said bars having radial driving surfaces overlapping and abutting the side surfaces of at least some of said protrusions in positive driving relationship to positively drive said protrusions at the same speed as said driving surfaces and circumferential surfaces engaging the end surfaces of at least some of said protrusions to limit the overlapping of said bars and said protrusions to prevent substantial extraneous contact between said cage and said belt, said protrusions being slidable vertically along said bars while said cage rotates to positively drive said belt, and
• secondary drive means synchronized with said primary drive means and positively engaging said belt at a first location along said planar approach portion closely adjacent said one end of said helical portion and at a second location along said planar exit portion closely adjacent said other end of said helical portion to cause the belt to travel at the same speed at said first and second locations, said secondary drive means having forwardly facing drive surfaces engaging said belt in forward driving relation and rearwardly facing retarding surfaces engaging said belt in rearward retarding relation while said belt moves in a planar path along said approach and exit portions, said first and second locations being positioned to maintain a substantially fixed length of belt extending between said one end and said other end of said helical portion to enable said belt to be positively driven smoothly through said loops by said cage under substantially minimal tension and substantially minimal driving pressure exerted by said cage.