GB2082698A

GB2082698A - Torque limiting coupling

Info

Publication number: GB2082698A
Application number: GB8125777A
Authority: GB
Original assignee: Excel Corp
Current assignee: Cargill Meat Solutions Corp
Priority date: 1980-08-25
Filing date: 1981-08-24
Publication date: 1982-03-10
Also published as: JPS5773230A; DE3133423A1; HK5886A; GB2082698B

Abstract

A torque limiting coupling for transmitting torque between a tubular member 10 and a shaft 16 is provided which is particularly suited for use as a conveyor roller. The shaft 16 extends axially through the tubular member 10 and is rotatably mounted in the tubular member at each end by a bearing assembly 18, 20. An annular retainer 30 is mounted between the shaft 16 and the inner bore of the tubular member 10 and has three radial openings 36 formed through it. A resilient member 38 having a circular outer periphery is positioned in at least one and preferably in each radial opening 36 in the retainer 30 so that the retainer 30 maintains the resilient members 38 in a circumferentially spaced apart relationship. The diameter of said resilient member 38 is greater than the distance between at least a portion of the outer periphery of the shaft 16 and the inner bore of the tubular member 10 so that torque can be transmitted between the shaft 16 and tubular member 10. The resilient members 38, however, are sufficiently diametrically compressible to enable the shaft 16 to rotate with respect to the tubular member 10 when the torque between the shaft 16 and tubular member 10 exceeds a predetermined amount. Two or more retainers 30 can be used with a single coupling to increase the torque drive for the coupling. <IMAGE>

Description

SPECIFICATION Torque limiting coupling The invention relates generally to torque overload or torque limiting couplings and, more particularly, to such a coupling to be used as a conveyor roller.

In existing roller conveyor systems a plurality of parallel and spaced apart rollers are mounted on a frame and together define the track or line for the conveyor system. In one type of previously known roller conveyor system, one or more rollers are continuously power driven while the remaining rollers are supporting or guiding rollers which are mounted on the frame for free rotation about their axes. In the event of jamming of the articles transported by the conveyor system, damage can result to the articles or even to the conveyor system itself since one or more rollers are continuously power driven. Thus, with this type of previously known roller conveyor system, it is necessary for an operator to be present constantly at the controls for the conveyor system in order to stop the system immediately in the event of jamming.

Also the construction of these conveyors makes them difficult if not impossible to curve the tract or to provide "S" curves which are sometimes advantageous.

The Applicant of the present application is the owner of U.S. Patent Nos. 3,942,338 and 4,056,953 directed to roller conveyor systems in which one or more of the conveyor rollers is a torque overload or torque limiting coupling which automatically releases and prevents damage in the event of jamming on the conveyor line.

As disclosed in these patents, the torque limiting coupling comprises a tubular cylindrical member having a shaft extending axially through it. The shaft is rotatably mounted at each end of the tubular member in a pair of spaced bearing assemblies. One or more resilient members having a circular outer periphery are then positioned between the outer peripheral surface of the shaft and the inner bore surface of the tubular member.

Furthermore, the diameter of the resilient member is greater than the narrowest distance between the outer periphery of the shaft and the inner bore of the tubular member so that the resilient member or members are compressed between the shaft and the tubular member, thus providing a driving connection between the shaft and tubular member. The resilient members, are however sufficiently diametrically compressible to permit the shaft to rotate independently of the tubular member when the torque between the shaft and tubular member exceeds a predetermined amount, indicative of jamming on the conveyor line.

The point at which release of the coupling occurs can be varied by varying the number of resilient members positioned between the outer periphery of the shaft and inner bore surface of the tubular member. Thus, a greater torque between the shaft and tubular member is required to release the coupling when two resilient members are used than when a single resilient member of the same type is used. However, when a large number of resilient members are used in order to obtain a large drive torque, the resilient members tend to rub against and interfere with each other.

This interference or rubbing between the resilient members results in wear and also undesirably results in a reduced and uneven torque release point for the coupling.

When the resilient member is in the form of a tube, it has been found that the resilient member has a tendency to become wrapped around the shaft or become twisted thus varying the torque transmitted between the shaft and the tubular member. Tubular resilient members also tend to flatten when subjected to heavy loads and over a long period of time they tend to remain in a flattened position thereby producing undesirable torque transmitting characteristics.

The invention provides an improved torque overload or torque limiting coupling which is particularly suitable for use in a conveyor roller system.

According to the invention a torque overload coupling comprises a tubular member; a shaft extending axially through said tubular member; first bearing means for rotatably connecting said shaft to said tubular member; second bearing means for rotatably connecting said shaft to said tubular member at a position axially spaced from said first bearing means; at least two resilient members having a circular outer periphery, said resilient members being positioned between said bearing means and between the outer periphera' surface of said shaft and the inner bore surface of said tubular member; means for holding said resilient members at predetermined circumferentially spaced positions with respect to each other while permitting said resilient members to rotate about their own axes, the diameter of each resilient member being greater than the distance between at least a portion of the outer peripheral surface of said shaft and the inner bore surface of the tubular member and said resilient members being sufficiently diametricaly compressible to enable said shaft to rotate relatively to said tubular member when the torque between said shaft and said tubular member exceeds a predetermined amount.

In brief, the torque overload coupling in accordance with the present invention comprises a tubular member having a shaft extending axially through it. A first bearing assembly rotatably connects one end of the tubular member to the shaft and, similarly, a second bearing assembly rotatably connects the opposite end of the tubular member to the shaft so that the shaft and tubular members are concentric with each other. An annular retainer is secured within the inner bore of the tubular member between the bearing assemblies and has an axial bore through which the shaft extends and can freely rotate with. In addition, at least two and preferably three circumferentially spaced radial openings are formed through the annular retainer.A resilient member having a circular outer periphery is positioned within at least one and preferably each radial opening of the retainer so that the retainer entraps and retains the resilient members in a circumferentially spaced apart position with respect to each other. Each resilient member, furthermore, has a diameter which is greater than the distance between at least a portion of the outer periphery of the shaft and the inner bore surface of the tube. The resilient members are thus compressed between the shaft and tubular member and function to drivingly connect the shaft and tubular member together. The resilient members, however, are sufficiently diametrically compressible to permit the shaft to rotate independently from the tubular member when the torque between the shaft and the tubular member exceeds a predetermined amount.

The retainers are dimensioned so that one or more retainers can be positioned between the bearing assemblies in order to vary the torque release of the coupling.

The retainers by keeping the resilient members separated prevent them from rubbing against each other thereby reducing wear and heat. Reducing the heat and the lateral support provided the resilient members by the retainer reduces the flattening of the resilient members. When tubular or cylindrical resilient member are utilized, the retainer keeps them aligned and prevents the resilient members from becoming twisted or wrapped around the shaft.

A better understanding of the invention will be had upon reference to the following detailed description when read in conjunction with the accompanying drawings, wherein like reference characters refer to like parts throughout the several views, and in which: Figure 1 is an exploded view illustrating a preferred embodiment of the torque overload coupling in accordance with the present invention; Figure 2 is a cross sectional view taken of the preferred embodiment of the coupling and showing the operation of the coupling in a torque transmitting mode; and Figure 3 is a view similar to Figure 2 but showing the preferred form of the torque overload coupling in a torque overload mode.

With reference to Figures 1 and 2, a preferred embodiment of the torque overload coupling in accordance with the present invention comprises an elongate tubular member 10 having an inner circular bore 12. An enlarged diameter portion 14 (Figure 1) of the bore 12 is formed at each axial end of the tubular member 10.

An elongate shaft 1 6 is positioned axially through the tubular member 10 and is coaxially rotatably mounted in the tubular member 10 by two bearing assemblies 18 and 20 (Figure 1). The first bearing assembly 1 8 is positioned around the shaft and within the enlarged diameter portion 14 of the bore 12 at one end of the tubular member 10.Similarly, the other bearing assembly 20 is positioned around the shaft 1 6 and within the enlarged diameter portion 14 of the inner bore 12 at the opposite axial end of the tubular member 1 0. The bearing assemblies 1 8 and 20 can be of any conventional construction and, with the shaft 16 mounted to the tubular member 10 by the bearing assemblies 18 and 20, the shaft 1 6 and the tubular member 10 can rotate independently of each other. In addition, the shaft 1 6 protrudes outwardly from at least one end of the shaft for a reason to be subsequently described.

As illustrated in the drawings, the shaft 1 6 has a polygonal cross sectional shape thus having a plurality of flat portions 22 and an edge 24 between each adjacent pair of flats 22. The diameter of the shaft 1 6 is much less than the diameter of the inner bore 12 of the tubular member 10 thus forming a space 26 between the outer peripheral surface of the shaft 1 6 and the surface of the inner bore 12 of the tubular member With reference still to Figures 1 and 2, a tubular and cylindrical retainer 30 having an axial throughbore 32 is positioned coaxially within the tubular member inner bore 12 and between the bearing assemblies 1 8 and 20.The retainer throughbore 32 is somewhat larger than the widest diametrical width of the shaft 1 6 so that the shaft 1 6 can freely rotate within the retainer throughbore 32.

In the preferred form of the coupling in accordance with the invention, the outer diameter of the retainer 30 is substantially the same as the diameter of the tubular member inner bore 12 so that the retainer can be positioned within the tubular member inner bore 12 and, once positioned, frictionally held in place coaxially with the tubular member 10. Alternatively, however, the outer diameter of the retainer 30 is less than the diameter of the tubular member inner bore 12 so that the retainer 30 can rotate within the inner bore 12.

The retainer 30 has at least two, and preferably three radial openings 36 formed through it so that each opening 36 is open to the retainer inner bore 32 and also to the outer periphery of the retainer 30. In addition, the radial openings 36 are circumferentially equidistantly spaced apart from each other around the circumference of the retainer 30.

The torque overload coupling further comprises at least one resilient member 38 having a circular outer periphery 40. As illustrated in the drawings, the resilient member 38 is cylindrical in shape, although other shapes, such as spherical, can also be used. The resilient member 38 can also be tubular rather than solid as shown. In addition, the resilient member 38 is dimensioned to fit within one of the radial openings 36 of the retainer 30 sov that at least a portion of the resilient member 38 can protrude into the retainer inner bore 32 as shown in Figure 2. The length of each cylindrical resilient member is greater than its diameter so that the retainer radial openings 36 are generally rectangular in shape having their longer axis extending parallel to the axis of the tubular member 10.The resilient members 38 can be made from any of a wide variety of different materials.

With reference now particularly to Figure 2, the diameter of the resilient member 38 is greater than the radial distance between any one of the edges 24 of the shaft 16 and the inner bore 12 of the tubular member 10. Thus, upon rotation of the shaft 1 6 by any conventional means, the resilient member is compressed between the shaft 16, the inner bore 12 of the tubular member 10 and against the retainer 30 and acts as a resilient wedge so that torque transmission between the shaft 1 6 and the tubular member 10 is effected.

Alternatively, the tubular member 10 can function as the drive unit while the shaft 16 acts as the driven unit whereby torque would be-transmitted from the tubular member 10 and to the shaft 16.

With reference now to Figure 3, the resilient members 38 are sufficiently diametrically compressible so that when the torque between the tubular member 10 and the shaft 1 6 exceeds a predetermined amount, the resilient members 38 are diametrically compressed and each rolls over one edge 24 of the shaft 1 6 and to the next flat 22 of the shaft 1 6. Thus, the tubular member 1 0 can be held stationary despite the continued rotation of the shaft 1 6 and, when this occurs, the resilient members 38 are continually being diametrically compressed and will roll over the edges 24 of the shaft 1 6 untii the torque between the shaft 1 6 and tubular member 10 falls below the predetermined amount.When this occurs, the shaft 1 6 again rotatably drives the tubular member 1 0.

The actual torque at which the torque overload coupling releases, is the function of the number of resilient members 38, the diameter of the resilient members 38 and the material which the resilient members 38 are constructed. Moreover, if desired, two or more retainers 30, each having one or more resilient members 38 can be positioned between the bearing assemblies 18 and 20 to increase the drive torque of the coupling.

In operation, the retainer 30 maintains the resilient members 38 at a predetermined and circumferentially spaced relationship with respect to each other and thus prevents the resilient members 38 from rubbing or otherwise contacting each other. As such the retainer 30 ensures an even and extremely predictable torque release for the torque coupling. In addition, the retainer 30 provides a wider surface against which the resilient members 38 can compress during the torque transmission mode for the coupling thus enabling greater torque transmission for the coupling.

The retainer supports the sides of the resilient member by reducing the tendency of the members 38 to flatten.

Although the shaft 1 6 has been described as polygonal in cross sectional shape, the shaft 1 6 can alternatively be of any convenient shape provided that the resilient members 38 are compressed between the outer peripheral surface of the shaft 1 6 and the surface of the tubular member inner bore 12 along at least some portion of the shaft 1 6. For example, the shaft 1 6 could even be round in cross sectional shape as long as the diameter of the resilient members 38 is greater than the distance between the outer periphery of a round shaft and the inner bore 1 2 of the tubular member 10. When a polygonal shaft is used, a slight puising will occur as the edges of the shaft roll past the resilient members 38. This is advantageous in some installations.The retainer 30 ensures an equal spacing of the resilient members 38 and thus an equal spacing between pulses when a polygonal shaft is used.

Similarly, although the resilient members 38 have been shown and described as being cylindrical in shape, other shapes for the resilient members 38 can also be employed provided that the resilient member 38 has a circular outer periphery. For example, spherical resilient members could also be used in lieu of the cylindrical resilient members 38.

Although the coupling of the present invention is adaptable for a number of different uses, it has been found particularly advantageous for use as a conveyor roller in an accumulating roller conveyor system. By utilising the coupling in this fashion, the shaft 1 6 can be continuously rotatably driven via the shaft portion extending outwardly from the tubular member. In the event of jamming on the conveyor line, the conveyor rollers can remain stationary despite the continued rotation of the shaft 1 6 and without damage to either the articles transported by the conveyor line or damage to the conveyor system.

Claims

1. A torque overload coupling comprising a tubular member; a shaft extending axially through said tubular member; first bearing means for rotatably connecting said shaft to said tubular member; second bearing means for rotatably connecting said shaft to said tubular member at a position axially spaced from said first bearing means; at least two resilient members having a circular outer periphery, said resilient members being positioned between said bearing means and between the outer peripheral surface of said shaft and the inner bore surface of said tubular member; means for holding said resilient members at predetermined circumferentially spaced positions with respect to each other while permitting said resilient members to rotate about their own axes, the diameter of each resilient member being greater than the distance between at least a portion of the outer peripheral surface of said shaft and the inner bore surface of the tubular member and said resilient members being sufficiently diametrically compressible to enable said shaft to rotate relatively to said tubular member when the torque between said shaft and said tubular member exceeds a predetermined amount.

2. A coupling as claimed in Claim 1 wherein said holding means comprises an annular retainer positioned within the inner bore of the tubular member and having a throughbore through which the shaft extends and can freely rotate, said retainer having at least two circumferentially spaced radial openings, one resilient member being positioned within each retainer opening.

3. A coupling as claimed in Claim 2 wherein said retainer has an axial length less than one half the axial distance between said bearing means so that two retainers can be positioned around said shaft between said bearing means.

4. A coupling as claimed in Claim 2 wherein said retainer is secured to and rotates in unison with said tubular member.

5. A coupling as claimed in any preceding claim wherein said resilient members are cylindrical and have their axes substantially parallel to but radially offset from the axis of the shaft.

6. A coupling as claimed in any preceding claim wherein said shaft is polygonal in cross section.

7. A coupling as claimed in any preceding claim wherein said bearing means are disposed at opposite ends of the tubular member.

8. A coupling as claimed in Claim 1 in which there are at least three circumferentially spaced resilient members positioned between the outer peripheral surface of said shaft and the inner bore of said tubular member.

9. A coupling as claimed in Claim 8 wherein said resilient members are circumferentially equidistantly spaced from each other.

10. A coupling as claimed in any preceding claim wherein the coupling is a conveyor roller.

11. A conveyor roller for an accumulating conveyor, said roller comprising a tubular member" a shaft extending axially through said tubular member, bearing means for rotatably connecting said shaft to said tubular member, at least one resilient member having a circular outer periphery being positioned between the outer peripheral surface of said shaft and the inner bore surface of said tubular member, the diameter of said resilient member being greater than the distance between at least a portion of the outer peripheral surface of said shaft and the inner bore surface of the tubular member to transmit torque between said shaft and said tubular member, and an annular retainer positioned within the inner bore of the tubular member and having a throughbore through which the shaft extends and can fully rotate, said retainer having at least one radially disposed opening, said resilient member being positioned within said retainer opening.

12. A torque overload coupling constructed and arranged substantially as described herein and shown in the accompanying drawings.