WO2007090149A2

WO2007090149A2 - Low friction, direct drive pin conveyor belt

Info

Publication number: WO2007090149A2
Application number: PCT/US2007/061369
Authority: WO
Inventors: Michael Degroot
Original assignee: Thermodrive Llc
Priority date: 2006-01-31
Filing date: 2007-01-31
Publication date: 2007-08-09
Also published as: WO2007090149A3; WO2007090149B1

Abstract

A thermoplastic endless belt has a smooth outer surface and an inner surface in which is formed a plurality of holes spaced at a given hole pitch. The holes are adapted to engage a pulley with circumferentially spaced pins having a pin pitch greater than the hole pitch. According to one embodiment, the holes are oblong, and the pins are cylindrical. Because of the difference in the hole pitch and the pin pitch and relative dimensions of the hole and pins, the belt can stretch to a maximum allowable elongation without detrimentally affecting the operation of the conveyor.

Description

LOW FRICTION, DIRECT DRIVE PIN CONVEYOR BELT

BACKGROUND OF THE INVENTION CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application Serial No. 60/743,190, filed January 31, 2006, which is incorporated herein in its entirety.

Field of the Invention

[0001] The invention relates to endless belts for conveyors and, more particularly, to a thermoplastic endless belt driven by a pulley having pins that engage holes in the belt.

Description of the Related Art

[0002J One type of conveyor belt is a pin belt comprising a continuous surface on one side and holes on the other side adapted to engage pins on a drive pulley, much like in the manner in which a dot-matrix printer advances paper. Because the belt has holes rather than teeth or other structures extending from the belt, as in toothed belts, for engaging the drive pulley, the pin belt can be made relatively thin and flexible. As a result, pin belts can be used in applications where small radius pulleys and nose bars are utilized. For example, a knife-edge nose bar, which has a bar with a radius as small as 1/8 inch, is commonly employed at a transfer point between two conveyors because the small radius allows a smaller gap between two conveyors. Furthermore, because pin belts can be made thin and, thereby, lightweight, they are often used for scale conveyors, where the conveyed products are weighed while on the conveyor belt. In these applications, the belt must be lightweight so that the belt adds minimal load to the scale and under minimal tension so that the belt does not support any of the product weight. [0003] hi prior art pin conveyor belts, the spacing between the holes of the belt, or hole pitch, is about equal to the spacing between the pins of the drive pulley, or pin pitch. Consequently, when the belt is not tensioned, the holes and the pins align longitudinally, whereby the holes receive the pins when the belt wraps around the drive pulley. As the drive pulley rotates, the pins received by the holes transfer torque from the drive pulley to the belt to advance the belt. Problems arise, however, when the belt stretches, such as due to the weight of the conveyed products. Belt stretching increases the hole pitch such that the hole pitch becomes greater than the pin pitch. As a result, the holes and pins are no longer longitudinally aligned, and torque cannot be properly transferred from the drive pulley to the belt through the pins and the holes. To minimize belt stretching, the products conveyed on pin belts are limited to relatively lightweight products, and the belts are relatively expensive, non-stretching composite belts reinforced with a woven fabric layer.

[0004] The low tension, direct drive thermoplastic toothed belt disclosed in U.S. Patent Application No. 60/593,493, which is incorporated herein by reference in its entirety, alleviates the problems associated with belt stretching. This type of belt is a thermoplastic belt having a smooth continuous surface on one side and teeth on the other side adapted to engage grooves or sheaves in a drive sprocket. To account for belt stretching, it has been determined that the tooth pitch of the belt must be less than the sheave pitch of the drive sprocket at less than maximum elongation of the belt. Also, the sprocket pitch must equal the pitch of the belt at maximum elongation, give or take a fraction of a percent. Moreover, to ensure that the belt teeth are positioned to enter the sprocket sheaves, the longitudinal width of each sheave in the sprocket must exceed the belt tooth longitudinal width at least by the amount of distance generated by elongating the belt the maximum allowable amount over the span of the belt wrap. As a result of the pitch and width differences, the teeth and the sheaves will be longitudinally aligned as long as the elongation is at or below the maximum elongation.

[0005] Due to the pitch difference between the belt and the sprocket, only one belt tooth will be driven by a sprocket sheave at any given moment. It has been found that this engaged tooth is always the tooth that is about to exit the sprocket. For all subsequent belt teeth that enter the sprocket sheaves at any given moment, there is a gap between the driving face of the belt tooth and the driving face of the sprocket sheave, and that gap progressively increases in size for each successive tooth. Consequently, as the exiting tooth disengages from the drive sprocket, there remains some amount of gap between the following belt tooth, i.e., the trailing tooth, and the face of its respective sprocket sheave. At this time, the sprocket continues to rotate relative to the belt without moving the belt, and the effective drive characteristics are lost until the driving face of the sheave abuts the driving face of the trailing tooth. In other words, the sprocket rotates while the belt slips until a tooth engages again. Discounting any momentum of the belt and any friction between the belt and the sprocket, the belt will effectively stop for a brief moment until the following sheave engages the trailing tooth, which thereby becomes the new "exit tooth".

[0006] Some slip between the belt and the sprocket is what enables a direct drive application to work. This temporary disengagement of belt teeth from sprocket sheaves causes the average belt speed to be less than the average sprocket speed, hi fact, the average belt speed is less than the sprocket speed by the percentage of elongation that is still available in the belt (max elongation - current elongation). Because of this necessary slip, any friction between the sprocket and the belt will compromise the benefits of direct drive. Friction between the belt and the sprocket will retard slippage and can cause the trailing tooth to miss the sprocket sheave altogether. To avoid such friction, the belt and the sprocket can be made of or coated with anti-friction materials, the sprocket can be designed such that the belt and sprocket have reduced contact area between the sheaves, and the belt is preferably maintained under low tension.

[0007] Although the above-described low tension, direct drive thermoplastic toothed belt does not suffer from the stretching problems associated with the pin belts, the toothed belt is not suitable for use in the applications that utilize the pin belt. The toothed belt is relatively thick due to the projecting teeth and, therefore, cannot be used -where small radius pulleys and nose bars are employed. Furthermore, the toothed belt is too heavy for scale conveyor applications.

SUMMARY OF THE INVENTION

[0008] According to the invention, a low friction, direct drive pin conveyor belt is adapted for use in a pin belt conveyor of the type comprising a drive pulley having a plurality of pins extending therefrom. The belt is stretchable along its length and has a plurality of holes spaced from each other to receive the pins as the belt wraps around the pulley. Each hole is longitudinally elongated to accommodate stretch in the belt and still enable the holes to r-eceive the pins. Preferably, the pulley pins and the belt holes are equidistantly spaced, respectively, from each other and the pitch of the belt holes is less than the pitch of the pulley pins when the belt is not stretched. Similarly, when the belt is at maximum allowable stretch, the hole pitch and the pulley pitch are nearly equal.

[0009] hi one aspect of the invention, the lateral width of the holes is slightly greater than the lateral width of the pins. Preferably, the belt will slip relative to the pulley. The inside surface of the belt, for example, can be coated with friction reducing material.

[0010] In another aspect of the invention, one of the holes will be an exit hole so that when the belt is mounted to a pulley, a position limiter is disposed near the exit hole. Preferably, the holes are configured in two longitudinal lines, hi another variation, the pins are raked toward the direction of movement of the pulley.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

[0011] Fig. 1 is a perspective view of a pin belt conveyor according to the invention. [0012] Fig. 2 is a side view of a pulley in the pin belt conveyor of Fig. 1. [0013] Fig. 3 is a top view of the pulley of Fig. 2.

[0014] Fig. 4 is a side view of a portion of the belt in the conveyor of Fig. 1. [0015] Fig. 5 is a plan view of the portion of the belt of Fig. 4. [0016] Fig. 6 is a side view of one pulley and a portion of the belt of Fig. 1, in cross section, showing the inter-engagement of the belt with the pulley. [0017] Fig. 7 is a second embodiment of the in belt conveyor according to the invention with the belt shown in phantom. [0018] Fig. 8 is a third embodiment of a portion of the belt conveyor according to the invention with the belt shown in cross section.

[0019] Fig. 9 is fourth embodiment of the belt conveyor according to the invention with the belt shown in phantom.

[0020] Fig. 10 is a fifth embodiment of the belt conveyor according to the invention.

[0021] Fig. 11 is another embodiment of the pulley for the belt conveyor of any of the foregoing embodiments.

DETAILED DESCRIPTION

[0022] A low tension, direct drive pin conveyor belt according to the invention provides a thin and flexible conveyor belt that alleviates problems caused by stretching of the prior art pin belts. The inventive pin belt incorporates the drive principles of the low tension, direct drive toothed belt discussed in the background of the invention to account for belt stretching. Because the pin belt can sustain a predetermined amount of stretch, the pin belt can be made with relatively low cost materials and processes, as well as being hygienic. In addition, conveyors with a pin belt drive according to the invention are robust and can support heavier loads than conventional pin belt conveyors. [0023] Referring now to the figures, Fig. 1 illustrates a first embodiment of a conveyor 10 comprising an endless pin belt 12 in a typical installation between two sets of pulleys 14, 16, wherein each of the sets of pulleys is mounted for rotation on a respective shaft 15, 17. At least one of the pulley sets, e.g. the pulley set 14, comprises a pair of substantially identical, spaced drive pulleys 18; the other pulley set 16 comprises a pair of substantially identical, spaced idler pulleys 20.

[0024] As shown in Figs. 2 and 3, each pulley 18, 20 has a plurality of radially extending pins 22 spaced around its circumference. The pins 22 can have any suitable shape and are shown in the illustrated embodiment as trapezoidal. Other exemplary shapes for the pins 22 include, but are not limited to, cylindrical, conical, frustoconical, rectangular, and square. Each of the pins 22 in this embodiment has a driving face 24 and an opposed, non-driving face 26; thus, the driving face 24 of one of the pins 22 faces the non-driving face 26 of an adjacent pin 22. The driving face 24 and the non-driving face 26 are inclined according to a pin face angle oq and joined at their upper edges by a plateau 28. For the trapezoidal pins 22, an exemplary radial height Hj and lateral width Wi for each of the pins 22 for a pulley 18, 20 with a radius Ri of about 2" are about 0.079" and about 0.250", respectively. Further, a longitudinal width W₂ of each of the pins 22 increases from a minimum longitudinal width W2"¹"¹ at the plateau 28 to a maximum longitudinal width W2^raax at the circumference of the pulley 18, 20, and an exemplary range of the longitudinal width W₂ for each of the pins 22 is from about 0.063" to about 0.113". To continue with the same example, an exemplary pin face angle αi and plateau longitudinal width W3 are about 35° and 0.063", respectively. [0025] Referring now to Figs. 4 and 5, the pin belt 12 comprises an inside surface 30 and an outside surface 32 joined at side edges 34, 36. According to one embodiment of the invention, the belt 12 is relatively thin and is typically made of a thermoplastic material such as Pebax^® resin, polyester, or polyurethane. An exemplary belt 12 has a lateral width W₄ defined between the side edges 34, 36 of about 12" and a thickness Ti defined between the inside surface 30 and the outside surface 32 of about 0.039". The outside surface 32 is fairly smooth and free of discontinuities, and a plurality of holes 38 are formed through the belt 12 in a pair of lines, with each of the lines parallel to and adjacent to one of the side edges 34, 36. Within each line, the holes 38 are equidistantly spaced from one another, and each hole 38 has a driving surface 40 and an opposed non- driving surface 42. The holes 38 can have any suitable geometry and are shown in the illustrated embodiment as rectangular. Other exemplary geometries for the holes 38 include circular, oblong, and square. For the rectangular holes 38, an exemplary lateral width W₅, longitudinal width W₆, and depth Dj for each of the holes 38 for the exemplary belt 12 having the width W₄ and the thickness T₁ of about 12" and 0.039" respectively, are about 0.375", 0.250", and 0.039", respectively. Although shown in the figures as extending completely through the thickness T₁ of the belt 12, the holes 38 can extend only partially through the belt 12, if desired. The holes 38 receive the pins 22 of the pulleys 18, 20 as the belt 12 wraps around the pulleys 18, 20. In this configuration, the upper span of the belt 12 will carry loads as the belt 12 travels in the direction of arrow 44 shown in Fig. 1. Furthermore, the driving face 24 and the non-driving face 26 of the pins 22 in the illustrated embodiment are symmetrical; thus, the belt 12 can be driven in the opposite direction by rotating the drive pulleys 18 in a direction opposite the arrow 44. [0026] Referring specifically to Fig..4, the holes 38 of the belt 12 have a pitch P i defined as the distance between the centerlines of adjacent holes 38. The belt pitch Pi is measured along a belt pitch line 50, which corresponds to the neutral bending axis of the belt 12. As the belt 12 bends around the pulley 18 or 20, the neutral bending axis is the imaginary plane on one side of which the belt material is under compression and on the other side of which the belt material is under tension.

[0027] Similarly, the pins 22 of the pulley 18, 20 have a pitch P₂ defined as the arc length between centerlines of adjacent pins 22, measured along a pulley pitch circle 52, as shown in Fig. 2. The pulley pitch circle 52 in this case corresponds to the belt pitch line 50 as the belt 12 wraps around the pulley 18, 20. In other words, the pulley pitch circle 52 has the same radius as the belt pitch line 50 as the belt 12 wraps around the pulley 18, 20.

[0028] According to one aspect of the invention, the hole pitch Pi is less than the pin pitch P₂ when the belt 12 is at less than a maximum allowable elongation to account for. belt stretching. At the maximum allowable elongation, the pitches P₁, P₂ are equal, give or take a fraction of a percent. Accordingly, the difference between the pitches Pi, P₂ is determined by a desired maximum allowable elongation of the belt 12. For an exemplary belt 12 and pulley 18, 20 having the. dimensions given above and having an exemplary maximum allowable elongation of about 1.5%, the hole pitch Pi can be about 1.042", and the pin pitch P₂ can be about 1.057" when the belt 12 is in a natural state and completely unstretched. This exemplary pin pitch P₂ corresponds to an angular spacing between the pins 22 of about 30° and a total of 12 of the pins 22 on the pulley 18, 20. When the belt 12 stretches to the maximum allowable elongation, the hole pitch Pi increases to the pin pitch P₂, which in this example is about 1.057". [0029] To account for the difference in the pitches Pj, P₂, the longitudinal width W₆ of the holes 38 is greater than the longitudinal width W2 of the pins 22 by at least by a distance generated by elongating or stretching the belt 12 to the maximum allowable elongation over the span of the belt 12. Additionally, the lateral width W₅ of the holes 38 is slightly greater than lateral width Wi of the pins 22 so that the holes 38 receive the pins 22 in the lateral direction.

[0030J Because the hole pitch Pi is less than the pin pitch P₂, and the longitudinal width W₆ of the holes 38 is greater than the longitudinal width W₂ of the pins 22 to accommodate the difference in the pitches Pi, P₂, the pin belt 12 can stretch an amount equal to the maximum allowable elongation without hindering the operation of the conveyor 10. This concept is more fully explained below with respect to Fig. 6. [0031] Referring to Fig. 6, where the belt 12 is unstretched or stretched less than the maximum allowable elongation, only one of the holes 38 and the corresponding pin 22 actually transfer torque from the drive pulley 18 to the belt 12 to drive the belt 12. This hole 38 is an exit hole 60 that is about to exit the drive pulley 18, and the corresponding pin 22 is an exit pin 62. The driving face 24 of the exit pin 62 contacts the driving surface 40 of the exit hole 60 to transfer torque from the pulley 18 to the belt 12. Several other pins 22 are received by other holes 38, but because the hole pitch Pj is less than the pin pitch P₂, a gap 64 exists between the driving faces 24 of the other pins 22 and the driving surfaces 40 of the respective other holes 38. The gap 64 progressively increases in size for each successive hole 38 in the direction opposite the arrow 44. Additionally, the other holes 38 and the respective other pins 22 longitudinally align (i.e., the other holes 38 can receive the other pins 22) because the longitudinal width W₆ of the holes 38 is greater than the longitudinal width W₂ of the pins 22.

[0032] A trailing hole 66, which is the hole 38 adjacent to the exit hole 60 in the direction opposite the arrow 44, receives a trailing pin 68, which is the pin 22 adjacent to the exit pin 62 in the direction opposite the arrow 44. Due to the gap 64 between the trailing pin driving face 24 and the trailing hole driving surface 40, there is no torque transmission from the drive pulley 18 to the belt 12 at the moment the exit hole 60 disengages the exit pin 62. Thus, the drive pulley 18 continues to rotate while the belt 12 effectively stops for a brief period of time until the trailing pin driving face 24 abuts the trailing hole driving surface 40, whereby the trailing hole 66 and the trailing pin 68 become the new driving hole and the new driving pin, respectively. [0033] As the belt stretches from the state shown in Fig. 6, the hole pitch Pi increases, and each of the gaps 64 decreases. The operation of the conveyor 10, however, proceeds as just described, except that the period of time during which the belt 12 stops between when the exit hole 60 and the exit pin 62 disengage and when the trailing hole 66 and the trailing pin 68 become the new driving hole and the new driving pin is reduced because the gap 64 has decreased. The conveyor 10 can continue to operate until the belt 12 stretches beyond the maximum allowable elongation because, at this point, the hole pitch Pi becomes larger than the pin pitch P2, whereby the holes 38 are no longer able to receive the pins 22. Thus, the difference between the pitches Pi, P2 must be set based on the desired maximum allowable elongation.

[0034] The pulleys 18, 20 and the belt 12 are designed to permit minimal friction therebetween so that the drive pulley 18 does not pull the belt 12 with the drive pulley 18 when the exit hole 60 and the exit pin 62 disengage. The slip between the pulleys 18, 20 and the belt 12 is necessary for the drive mechanism to function properly. The inside surface 30 of the belt 12 can be coated with a friction reducing material, e.g. polytetrafluoroethylene (PTFE), also known as Teflon^®. The pulleys 18, 20 preferably have minimal surfaces contacting the belt 12 anywhere but at the pins 22. For example, the supporting structure between adjacent pins 22 can be recessed from the perimeter of the pulley 18, 20. The pulley 18, 20 can also have a narrower neck to reduce surface contact with the belt 12.

[0035] Referring now to Fig. 7, the conveyor 10 can further include a roller 70 positioned on the shaft 15 between the drive pulleys 18. The roller 70 spins freely on the shaft 15 and provides support to the pin belt 12 so that the pin belt 12 does not sag into the space between the pulleys 18. It also minimizes the likelihood of transmitting torque through friction with the pulleys or with the shaft. A similar roller 72 can be positioned on the shaft 17 between the idler pulleys 20.

[0036] As illustrated in Fig. 8, the conveyor 10 can further incorporate one or more position limiters 80, which are disclosed in the aforementioned and incorporated U.S. Patent Application No. 60/593,493 (the '493 application). The position limiter 80 is located near the natural exit point where the exit hole 60 of the belt 12 leaves the exit pin 62 of the drive pulley 18. Alternatively, the position limiter 80 can be located elsewhere, such as immediately prior to the exit point and at the trailing hole 66. The position limiter 80 is preferably a pair of rollers straddling either side of the pins, but the position limiter 80 can have any suitable form, as more fully described in the '493 application. [0037] hi the embodiments of the conveyor 10 of Figs 1-4, the holes 38 are shown as being arranged in two lines along the side edges 34, 36 of the belt 12, but it is within the scope of the invention for the belt 12 to have any number of lines of the holes 38 located in any position relative to the side edges 34, 36 of the belt 12. For example, an alternative embodiment of the conveyor 100, which is illustrated in Fig. 9, where components similar to those of the first embodiment conveyor 10 are identified with the corresponding numeral in the one hundred series, comprises a single line of the holes 138 located centrally between the side edges 134, 136 of the belt 112. Accordingly, the belt 112 is driven by a single drive pulley 118 at one end of the belt 112 and wraps around a single idler pulley 120 at the opposite end of the belt 112. hi this embodiment, the side edges 134, 136 are optionally supported by rollers 170, 172 positioned on both sides of the pulleys 118, 120, respectively, to prevent belt sagging at the belt edges 134, 136. [0038] The conveyor 10, 100 can further comprise more than one set of idler pulleys 20, as in a center drive conveyor 200 illustrated in Fig. 10. In Fig. 10, components similar to those of the first embodiment conveyor 10 are identified with the corresponding numeral in the two hundred series. The center drive conveyor 200 has a center set of drive pulleys 218 and two sets of idler pulleys 220, which are shown in the illustrated embodiment as smooth rollers but can also be pulleys with pins. As an example, each of the idler pulleys 220 can have a radius of about 0.5", and the distance between the sets of the idler pulleys 220 can be about 18". The advantages of the center drive conveyor 200 over the conveyors 10, 100 having only two sets of pulleys for a direct drive system are described in the '493 application.

[0039] The pins 22 on the drive and idler pulleys 18, 20 have been described above and shown in the figures as radially oriented. It is within the scope of the invention, however, to arrange the pins 22 in other suitable orientations. For example, in an alternative embodiment of a drive pulley 318, which is illustrated in Fig. 11 , where components similar to those of the first embodiment conveyor 10 are identified with the corresponding numeral in the three hundred series, the pins 322 rake forward. The pins 322 of the idler pulleys 320 can rake forward in a similar manner. [0040] By modifying current pin belts to incorporate the above-described drive system, the inventive pin belt can withstand a predetermined amount of belt stretching without detrimentally affecting the operation of the conveyor. Additionally, because the pin belts can sustain some stretching, they can be made with relatively inexpensive materials and processes, and be made hygienic. Furthermore, the conveyors with the inventive pin belts can handle heavier and more fluctuating loads than the prior art pin belt conveyors. Alternatively, the invention can be thought of as modifying the low friction, direct drive thermoplastic toothed belts disclosed in the '493 application so that they can be made thin, lightweight, and flexible due to the use of holes rather than projecting teeth and can be used in applications where these properties are essential, such as with small diameter pulleys and nose bars and in scale conveyors. [0041] While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.

Claims

CLAIMSWhat is claimed is:

1. A low friction, direct drive pin conveyor belt (12, 112) adapted for use in a pin belt conveyor (10) of the type comprising a drive pulley (18) having a plurality of pins (22, 322) extending therefrom, the belt being stretchable along its length and having a plurality of holes (38, 138) spaced from each other to receive the pins (22, 322) as the belt wraps around the pulley (18), characterized by each hole being longitudinally elongated to accommodate stretch the belt and still enable the holes to receive the pins.

2. A conveyor belt (12, 112) according to claim 1 wherein the pulley pins (22, 322) and the belt holes (38, 138) are equidistantly spaced, respectively, from each other and the pitch (Pi) of the belt holes is less than the pitch (P₂) of the pulley pins (22, 322) when the belt is not stretched.

3. A conveyor belt (12, 112) according to claim 2 wherein when the belt (12,

112) is at maximum allowable stretch, the hole pitch (Pi) and the pulley pitch (P₂) are nearly equal.

4. A conveyor belt (12, 112) according to any of claims 1-3 wherein the lateral width of the holes (38, 138) is slightly greater than the lateral width of the pins (22, 322).

5. A conveyor belt according to any of claims 1-4 wherein the belt (12) will slip relative to the pulley (18).

6. A conveyor belt (12, 112) according to any of claims 1 -5 wherein the inside surface (30) of the belt (12) is coated with friction reducing material.

7. A conveyor belt (12, 112) according to any of claims 1-6 wherein one of the holes (38, 138) an exit hole (38, 138) and the belt is mounted to a pulley (18), and further comprising a position limiter (80) disposed near the exit hole.

8. A conveyor belt (12, 112) according to any of claims 1-7 wherein the holes (38, 138) are configured in two longitudinal lines.

9. A conveyor belt (12, 112) according to any of claims 7-8 wherein the pins (322) are raked toward the direction of movement of the pulley (318).