Smooth-entry positive-drive spiral conveyor

Abstract

A spiral conveyor system with an entry ridge segment having a trailing ramped face for the smooth entry of a conveyor belt onto a helical path about a cylindrical drive drum. The entry ridge segment allows the inside edge of belt to ride up and over the ridge as the inside edge of the belt collapses entering the helical path and guides driven surfaces on the belt's inside edge into driving engagement with leading drive faces on generally vertical ridges on the drum's periphery.

Description

[0001] SMOOTH-ENTRY POSITIVE-DRIVE SPIRAL CONVEYOR

[0002] BACKGROUND

[0003] The invention relates generally to power-driven conveyors and more particularly to spiral conveyors in which a conveyor belt is positively driven in a helical path around a rotating drive cage and to a related method.

[0004] Positively driven spiral systems, in which drive structure on the periphery of a rotating drum engages structure on the inside edge of a conveyor belt, have been used to convey articles, such as foodstuffs and other materials, through cooled or heated environments. Spiral conveyors, in which a conveyor belt follows a helical path winding around a central cylindrical tower, drum, or cage, are used in freezers and ovens to provide a long conveying path with a small footprint. The periphery of the drum is formed by circumferentially spaced cage bars extending in length generally vertically from the bottom to the top of the drum or by a continuous cylindrical wall. Ridges formed on the cage bars or on the wall form drive structure that drives the radially inner edge of the belt. Because there is positive engagement between the regularly spaced drive structure on the drum and regularly spaced edge structure on the inside edge of the belt, there is no slip as in friction- driven overdrive spiral systems. No additional tensioning is needed, and frictional losses are less. But one problem with positively driven spiral systems is in cleanly engaging the belt with and disengaging it from the drive structure on the drum.

[0005] A common entry portion at the bottom of an upgoing spiral conveyor is shown in FIG. 6. Ridges 80 on the periphery 82 of a cylindrical drive drum 84 extend in length between the bottom 86 and the top 87 of the drive drum 84. The ridges 80 protrude outward from the periphery 82. The ridges 84 have leading faces 88 and trailing faces 89. Leading faces 88 drive a conveyor belt 90 up along a helical path around the drive drum 81. The profile of the periphery 82 without showing the ridges is shown at the left in FIG. 6. The periphery 82 has a constant-diameter lowermost portion 91 and a constant-diameter uppermost portion 93. The diameter of the lowermost portion 91 is greater than the diameter of the uppermost portion 93, which extends up the majority of the height of the drum. An intermediate portion 92 of the periphery is angled off vertical to extend from the upper end of the lowermost portion 91 to the lower end of the uppermost portion 93. Pointed lower tip ends 94 of the ridges 80 protrude outward of the lowermost portion 91 of the periphery 82. Raised bumps 96 separated from the tip ends 94 of the ridges 80 extend radially outward of the lowermost portion 91 and help align belt driven surfaces with the tip ends for initial engagement with the ridges 80.

[0006] It's important that the tip ends 94 of all the ridges 80 be at the same level. But positioning the ridges 80 correctly requires careful positioning of the ridges on the drum 84. When the tip ends 94 of the ridges 80 aren't at the same level, the inside edge of the belt 90 tangentially enters into initial engagement with the drum's periphery below, on, or atop a ridge 80. The inconsistent entry of the belt 90 into engagement with the ridges 84 means that engagement of the inside edge of the belt with the ridges won't always be smooth. Thus, the fact that it's difficult to meet the strict construction requirement that the tip ends 94 of the ridges 80 be level means that entry of the belt 90 onto the drum 84 won't be smooth in some installations.

[0007] SUMMARY

[0008] A spiral conveyor embodying features of the invention comprises a cylindrical drive drum that is rotatable about an axis of rotation and extends from a bottom to a top. The drive drum has circumferentially spaced ridges, each of which extends in length between the bottom and the top of the drive drum and radially outward of the axis of rotation to a ridgeline. Each of the ridges has a leading drive face in the direction of rotation of the drive drum. Each of the ridges has an entry segment nearest the bottom for an upgoing spiral and nearest the top for a downgoing spiral. The entry segment of each of the ridges has a trailing ramped face in the direction of rotation of the drive drum.

[0009] A method for driving a conveyor belt on a helical path around a drive drum comprises: (a) providing a cylindrical drive drum with a plurality of generally vertical drive ridges spaced apart circumferentially on the drive drum's periphery and extending in length between the top and the bottom of the drive drum to a ridge entrance end at one end wherein each of the drive ridges has a leading drive face and a trailing ramped face;

[0010] (b) rotating the drive drum about an axis of rotation; and (c) entering a conveyer belt into engagement with the drive ridges at a level above the level of the ridge entrance end for an upgoing spiral or at a level below the level of the ridge entrance end for a downgoing spiral so that driven surfaces on the inside of the conveyor belt can ride up and over the trailing ramped face and into positive engagement with the leading drive faces of the drive ridges as the inside edge collapses entering a helical path around the cylindrical drum drive.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] These and other features of the invention are described in detail in the following description, appended claims, and accompanying drawings.

[0013] FIG. 1 is an elevation view of a positively driven spiral conveying system with a first version of a drive drum.

[0014] FIG. 2 is a perspective view of a positively driven spiral conveying system with a second version of a drive drum.

[0015] FIG. 3 is a top plan view of a portion of the bottom tier of a spiral conveyor belt as it tangentially enters into engagement with a drive drum.

[0016] FIG. 4 is an elevation schematic of a portion of the periphery of a spiral conveyor as in FIG. 1 or FIG. 2 showing an extended ridge.

[0017] FIG. 5 is a cross section of the drive drum viewed along lines V-V of FIG. 4 to show the geometry of the ridge, and FIG. 5A is an enlarged view of the ridge's cross section.

[0018] FIG. 6 is a front elevation schematic of a portion of the periphery of a prior-art spiral conveyor also showing the profile of the periphery on the left.

[0019] DETAILED DESCRIPTION

[0020] One version of a spiral conveyor system is shown in FIG. 1. The spiral conveyor system comprises a cylindrical drive drum 10 with circumferentially spaced drive ridges 12 extending in length from the bottom 14 to the top 15 of the drum and radially outward to a ridgeline. The drive drum 10 is motor driven to rotate about an axis of rotation 16. The ridges 12 engage structure on the inside edge of a conveyor belt to positively drive the belt without slip around and up the drum along a helical path 18. The belt enters the helical path 18 tangentially into initial engagement with the ridges 12 at an entry portion 19 of the drum 10. The helical path 18 is defined by a conventional belt-supporting helical carryway (not shown) constructed around the drum's periphery 20. Alternatively, the helical path 18 could be established by a single-tier helical carry way at the bottom 14 supporting a stacker belt having stacker plates that support the belt tiers above.

[0021] Unlike the drive drum 10 of FIG. 1, which has a constant diameter D throughout its height, the drive drum 22 of FIG. 2 is a dual-diameter drum having a first diameter dl through most of its height in a main portion 26 and a greater second diameter d2 at the belt entry in an entry portion 27 at the bottom 24. The two constant-diameter portions 26, 27 of the drum 22 are connected by an intermediate portion 28 whose diameter varies from the first diameter dl at the junction with the main portion 26 to the second diameter d2 at the junction with the entry portion 27. The dual-diameter drum 22 decreases tension in the belt by allowing the belt to relax as the diameter decreases along the helical path. Spaced-apart ridges 30 extending radially outward of the drum's periphery 32 engage structure at the inside edge of a conveyor belt to drive the belt along a helical path up and around the cylindrical drum 22 rotating about its axis of rotation 34. Entry segments 35 of the ridges 30, which a belt initially engages, are on the entry portion 27 of the drum 22.

[0022] FIG. 3 shows the start of the bottom tier of a modular conveyor belt 36 as it tangentially enters into initial engagement with a drum 38 rotating about its axis of rotation 40 in a counterclockwise direction 42. The rows of belt modules 43 composing the belt 36 collapse at the inside edge 44 as they enter the helical path around the drum's periphery. The collapse of the belt rows at the inside edge 44 of the belt 36 occurs because the inside edge follows a shorter path around the drum 38 than the belt's outside edge 45. The circumferentially spaced-apart drive ridges 46 drivingly engage the trailing ends of driven surfaces 47 on the inside edge 44 of the belt 36 to drive the belt along the helical path up the drum 38. The driven surfaces can be formed on faces of the natural belt edge as in FIG. 3 or can be formed on teeth protruding from the natural belt edge.

[0023] FIG. 4 shows a conveyor belt 48 initially entering the entry portion 50 at the bottom 52 of a drive drum 54 rotating in a clockwise direction 56. The drive ridges 58 extend to ridge entrance ends 59 in the bottom 60 of the entry portion 50. The conveyor belt 48 enters the entry portion at a level 61 above the level of the ridge entrance ends 59. Thus, the conveyor belt 48 is guaranteed to engage the entry segment of a ridge 58 upon entry into the helical path. The belt 48 doesn't have to slide up into engagement with the tip end of the ridge as in FIG. 6 because it engages the ridges 58 on entry. As the inside edges of the rows of belt modules collapse, they are pulled forward at a speed slightly greater than the drum speed. A trailing ramped face 62 on each of the ridges 58 allows the collapsing structure on the inside of each belt row to slide up and over the ridge without getting caught. Once the rows are collapsed at the inside edge, a leading drive face 64 engages driven surfaces on the inside-edge belt structure to drive the belt 50 along the helical path. The structure of the ridge 58 is shown in FIG. 5. The ridge 58 is generally triangular, or wedge-shaped, in cross section with a trailing ramped face 62 intersecting a leading drive face 64 at an apex 66 defining the ridgeline. The apex 66 can be blunt as indicated by the dashed lines 67 in FIG. 5A to eliminate its sharp tip. In this example, the ridge 58 is formed on a plastic insert 68 having attachment structure in the form of arms 70 terminating in tabs 72 that allow the insert 68 to be snapped onto a metal cage bar 74 on the periphery of the drum. But other forms of attachment, such as screws, are possible.

[0024] Although the cross section of the ridge can be the same along its entire length, it's important that the ramped shape be present in an entry ridge segment on the entry portion of the drum's periphery to ensure a smooth entry of the belt into engagement with the ridges. The cross section of the ridges above the entry portion can differ from the cross section of the ridges in the entry portion. For example, the cross section of the ridges above the entry portion can be rectangular. In general the leading drive face of the ridge is generally continuous along its entire length on the periphery of the drive drum even if the cross section changes along its length. Small insubstantial discontinuities in the drive faces can occur if the ridges are made in sections or if parts of the ridges are formed on inserts that overlay other parts of the ridges.

[0025] Although the invention has been described with reference to an upgoing spiral conveyor system in which the belt enters the drum at the bottom, the ramped ridge design can also be used in downgoing spiral conveyors in which the belt enters at the top below the ridge entrance ends.

Claims

WHAT IS CLAIMED IS:

1. A spiral conveyor comprising: a cylindrical drive drum rotatable about an axis of rotation and extending from a bottom to a top and having a plurality of circumferentially spaced ridges each extending in length between the bottom and the top of the drive drum and radially outward of the axis of rotation to a ridgeline; wherein each of the ridges has a leading drive face in the direction of rotation of the drive drum; wherein each of the ridges has an entry segment nearest the bottom for an upgoing spiral and nearest the top for a downgoing spiral; and wherein the entry segment of each of the ridges has a trailing ramped face in the direction of rotation of the drive drum.

2. The spiral conveyor as claimed in claim 1 wherein the leading drive face of the entry segment intersects the trailing ramped face at the ridgeline of the entry segment.

3. The spiral conveyor as claimed in claim 1 wherein the cross section of the ridges is constant along their entire lengths.

4. The spiral conveyor as claimed in claim 1 wherein the cross section of the ridges in at least the entry segments is triangular in shape.

5. The spiral conveyor as claimed in claim 1 wherein the cylindrical drive drum has an entry portion with a first diameter, a main portion with a smaller second diameter, and an intermediate portion whose diameter decreases from the first diameter at the entry portion to the second diameter at the main portion and wherein the entry segments of the ridges are disposed on the entry portion.

6. The spiral conveyor as claimed in claim 1 comprising a conveyor belt that enters the helical path at a level at which the entry segments of the ridges are present.

7. The spiral conveyor as claimed in claim 1 comprising a conveyor belt driven along a helical path up or down the cylindrical drive drum by engagement of driven surfaces on an inside edge of the conveyor belt with the ridges, wherein the trailing ramped faces on the entry segments of the ridges allow the inside edge of the conveyor belt to ride up and over the ramped faces to align the driven surfaces with the leading drive faces of the ridges as the inside edge of the conveyor belt collapses forward as it enters the helical path.

8. A method for driving a conveyor belt on a helical path around a drive drum, the method comprising: providing a cylindrical drive drum with a plurality of generally vertical drive ridges spaced apart circumferentially on the drive drum's periphery and extending in length between the top and the bottom of the drive drum to a ridge entrance end at one end wherein each of the drive ridges has a leading drive face and a trailing ramped face; rotating the drive drum about an axis of rotation; entering a conveyer belt into engagement with the drive ridges at a level above the level of the ridge entrance end for an upgoing spiral or at a level below the level of the ridge entrance end for a downgoing spiral so that driven surfaces on the inside of the conveyor belt can ride up and over the trailing ramped face and into positive engagement with the leading drive faces of the drive ridges as the inside edge collapses entering a helical path around the cylindrical drum drive.

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