SHRINK CONVEYOR AND METHOD FOR ALLOWING SHRINK IN A CONTINUOUS STRIP

Abstract

A shrink conveyor and a method are provided for allowing shrink in a continuous strip. The shrink conveyor comprises a plurality of rollers, a frame that defines a plurality of roller positions, and a first drive member for driving the plurality of rollers. Each roller of the plurality of rollers comprises a first driven part that has a first drive profile that tapers. The first drive member is arranged for rotating the plurality of rollers through contact with the first driven parts at a rotation speed in a transmission ratio to the speed of the first drive member in such a way that the first drive member contacts the first driven part of each roller of the at least three rollers at a different diameter for each roller.

Claims

1-40. (canceled)

41. A shrink conveyor for allowing shrink in a continuous strip, the shrink conveyor comprising: a plurality of rollers; a frame that defines a plurality of roller positions fixed and spaced apart in a transport direction for holding the plurality of rollers in a mutually parallel orientation perpendicular to said transport direction; and a first drive member for driving the plurality of rollers, wherein each roller of the plurality of rollers comprises a roller body that is rotatable about a roller axis extending in an axial direction and a first driven part connected to said roller body coaxially to the roller axis, wherein the first driven part in a cross section parallel to the axial direction has a first drive profile, wherein the first drive profile for at least three rollers of the plurality of rollers tapers, wherein the first drive member is arranged for rotating the plurality of rollers through contact with said first driven parts at a rotation speed in a transmission ratio to the speed of the first drive member that is defined by a diameter of the first driven part at a contact position of the first drive member along the respective first drive profiles, wherein the first drive member is movable with at least a vector component in a lateral direction parallel to the axial direction of the plurality of rollers in such a way that the first drive member contacts the first driven part of each roller of the at least three rollers at a different diameter for each roller.

42. The shrink conveyor according to claim 41, wherein the first drive profile tapers at a taper rate that is different for each roller of the at least three rollers.

43. The shrink conveyor according to claim 41, wherein the first drive profiles for the at least three rollers differ in that each first drive profile tapers at a different taper angle relative to the respective roller axis.

44. The shrink conveyor according to claim 41, wherein the first driven part is at least partially conical, wherein the first driven parts of the at least three rollers have different conicities.

45. The shrink conveyor according to claim 42, wherein the taper rate increases or decreases for each subsequent roller of the at least three rollers in the transport direction.

46. The shrink conveyor according to claim 45, wherein the taper rate increases or decreases for each subsequent roller of the at least three rollers at least partially linearly.

47. The shrink conveyor according to claim 45, wherein the taper rate increases or decreases for each subsequent roller of the at least three rollers at least partially non-linearly.

48. The shrink conveyor according to claim 41, wherein the first drive profile for one or more rollers of the plurality of rollers downstream of the at least three rollers in the transport direction is cylindrical.

49. The shrink conveyor according to claim 41, wherein the first drive profile tapers differently for each roller of at least half of the plurality of rollers.

50. The shrink conveyor according to claim 41, wherein the first drive member is configured to remain parallel to the transport direction during said movement in the lateral direction.

51. The shrink conveyor according to claim 41, wherein the first drive profile tapers at a taper rate that is the same for each roller of the plurality of rollers.

52. The shrink conveyor according to claim 41, wherein the first drive member is configured to rotate between a neutral orientation in which the first drive member is parallel to the transport direction and a skewed orientation in which the first drive member is at an oblique angle to the transport direction.

53. The shrink conveyor according to claim 41, wherein the first drive member comprises an endless belt.

54. The shrink conveyor according to claim 41, wherein each roller of the at least three rollers comprise a second driven part connected to the roller body coaxially to the roller axis, wherein the second driven part in a cross section parallel to the axial direction has a second drive profile, wherein the second drive profile for the at least three rollers of the plurality of rollers tapers.

55. The shrink conveyor according to claim 54, wherein the taper rate of the second drive profile is the same as the taper rate of the first drive profile of the same roller for each roller of the at least three rollers.

56. The shrink conveyor according to claim 54, wherein the second drive profile is mirror symmetrical to the first drive profile of the same roller for each roller of the at least three rollers.

57. The shrink conveyor according to claim 54, wherein the second drive profile tapers in the same direction as the first drive profiles.

58. The shrink conveyor according to claim 54, wherein the first driven part and the second driven part are connected to the roller body at opposite ends of said roller body in the axial direction.

59. The shrink conveyor according to claim 54, wherein the shrink conveyor further comprises a second drive member for contacting the second driven parts of the plurality of rollers and rotating the plurality of rollers through said contact with said second driven parts.

60. The shrink conveyor according to claim 59, wherein the second drive member is movable with at least a vector component in the lateral direction.

61. The shrink conveyor according to claim 60, wherein the first drive member and the second drive member are configured to remain mutually parallel during said movement in the lateral direction.

62. The shrink conveyor according to claim 59, wherein the first drive member and the second drive member are configured to rotate between a neutral orientation in which the drive members are parallel to the transport direction and a skewed orientation in which the drive members are at an oblique angle to the transport direction.

63. The shrink conveyor according to claim 59, wherein the first drive member and the second drive member are mechanically coupled to move symmetrically in the lateral direction.

64. The shrink conveyor according to claim 41, wherein the plurality of roller positions is greater in number than the plurality of rollers.

65. A method for allowing shrink in a continuous strip with the use of a shrink conveyor according to claim 41, wherein the method comprises the steps of: positioning the at least three rollers in an equal number of roller positions of the plurality of roller positions; moving the first drive member with at least a vector component in the lateral direction to vary the transmission ratio for the at least three roller; and rotating the at least three rollers at different rotation speeds in accordance with the varied transmission ratio between the respective rollers and the first drive member.

66. The method according to claim 65, wherein the at least three rollers are positioned in equal number of roller positions such that the taper rate increases or decreases for each subsequent roller of the at least three rollers in the transport direction.

67. The method according to claim 66, wherein the taper rate increases or decreases for each subsequent roller of the at least three rollers at least partially linearly.

68. The method according to claim 66, wherein the taper rate increases or decreases for each subsequent roller of the at least three rollers at least partially non-linearly.

69. The method according to claim 65, wherein the method further comprises the step of keeping the first drive member parallel to the transport direction during said movement in the lateral direction.

70. The method according to claim 65, wherein the method further comprises the step of rotating the first drive member between a neutral orientation in which the first drive member is parallel to the transport direction and a skewed orientation in which the first drive member is at an oblique angle to the transport direction.

71. The method according to claim 65, wherein the at least three rollers are positioned in an equal number of roller positions of the plurality of rollers positions which are evenly spaced apart in the transport direction.

72. The method according to claim 65, wherein the at least three rollers are positioned in an equal number of roller positions of the plurality of rollers positions which are unevenly spaced apart in the transport direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The invention will be elucidated on the basis of an exemplary embodiment shown in the attached schematic drawings, in which:

[0057] FIG. 1 shows an isometric view of a shrink conveyor with a plurality of rollers according to a first embodiment of the invention;

[0058] FIG. 2 shows a top view of the shrink conveyor according to FIG. 1;

[0059] FIGS. 3 and 4 show cross sections of the shrink conveyor according to line III-III and line IV-IV, respectively, in FIG. 2;

[0060] FIG. 5 shows a top view of the shrink conveyor according to FIG. 1 with a different configuration of the plurality of rollers;

[0061] FIG. 6 shows a top view of the shrink conveyor according to FIG. 1 exposing the mechanism that drives the rollers;

[0062] FIG. 7 shows a top view of an alternative shrink conveyor according to a second embodiment of the invention;

[0063] FIG. 8 shows a top view of a further alternative shrink conveyor according to a third embodiment of the invention;

[0064] FIG. 9 shows a top view of a further alternative shrink conveyor according to a fourth embodiment of the invention; and

[0065] FIG. 10 shows an isometric view of a shrink conveyor according to the prior art.

DETAILED DESCRIPTION OF THE INVENTION

[0066] FIGS. 1-6 show a shrink conveyor 1 according to a first embodiment of the invention for allowing shrink in a continuous strip 9, in particular a tire component for tire building. In this exemplary embodiment, the tire component is a freshly extruded apex strip, having a substantially triangular cross section. As the apex strip leaves the extruder, it cools down and needs to be able to contract to allow for the elastomeric material to relax.

[0067] As shown in FIG. 1, the shrink conveyor 1 is a roller conveyor. The shrink conveyor 1 is positioned directly downstream of a pull-off conveyor 8 that pulls the continuous strip 9 from an extruder (not shown). At the downstream end of the shrink conveyor 1, a dancer roller 7 or another buffer member is provided to feed the continuous strip 9 in a loop to a subsequent station, for example a cooling drum (not shown). The shrink conveyor 1 comprises a base or a frame 2 with a frame body 20 and a plurality of frame slots 21 formed in said frame body 20 to define an array or a plurality of roller positions P1, P2, . . . , Pn. The roller positions P1, P2, . . . , Pn are spaced apart in a transport direction T. The roller positions P1, P2, . . . , Pn are fixed or stationary in the transport direction T. In other words, once placed, the rollers 3 rotate while remaining in their respective roller positions P1, P2, . . . , Pn in the transport direction T.

[0068] In this example, the roller positions P1, P2, . . . , Pn are evenly spaced apart. The shrink conveyor 1 further comprises a plurality of rollers 3 to be received or placed in said rollers positions P1, P2, . . . , Pn. When received in the plurality of roller positions P1, P2, . . . , Pn, the rollers 3 together form or define a plane of conveyance for the continuous strip 9. Note that the shrink conveyor 1 as shown in FIG. 1 has less rollers 3 than roller positions P1, P2, . . . , Pn. In particular, the rollers 3 are positioned with one empty roller position P1, P2, . . . , Pn between. Alternatively, all roller positions P1, P2, . . . , Pn may be occupied, or a different distribution of rollers 3 over the available roller positions P1, P2, . . . , Pn may be chosen. FIG. 5 shows an alternative configuration in which some of the rollers 3 are paired in directly adjacent roller positions P1, P2, . . . , Pn while others are spaced apart by one or more empty roller positions P1, P2, . . . , Pn.

[0069] The rollers 3 are exchangeably or interchangeably received in the frame slots 21, meaning that they can be detached and/or removed from the respective roller positions P1, P2, . . . , Pn to be repositioned within the shrink conveyor 1 or to be taken out and replaced by another roller 3. In particular, the frame slots 21 are open in an upward direction such that the rollers 3 can be freely taken out in said upward direction. This may also increase operator safety because of a reduced risk of pinching. The shrink conveyor 1 may be accompanied by a set of spare rollers 3 to replace one or more of the rollers 3 currently held in the frame 2.

[0070] As best seen in FIG. 2, each roller 3 comprises a roller body 30 that is rotatable about a roller axis R. The roller axis R defines an axial direction A. In this example, the roller body 30 is cylindrical or straight cylindrical. Alternatively, the roller body 30 may be crowned. The rollers 3, when received in the plurality of roller positions P1, P2, . . . , Pn, are mutually parallel. In other words, their roller axes R are mutually parallel. More in particular, it can be observed that the roller axes R extend in a lateral direction L parallel or substantially parallel to the axial direction A, and/or perpendicular or substantially perpendicular to the transport direction T. The frame 2 is preferably shaped or provided with an additional wall on opposite sides of the rollers 3 in the lateral direction L to enclose the rollers 3, thereby fixating them or preventing excessive movement of the rollers 3 relative to the frame 2 in said lateral direction L.

[0071] Each roller 3 is further provided with a first driven part 31 positioned or extending coaxially with respect to the roller axis R of the respective roller body 30. In this example, each roller 3 is further provided with a second driven part 32, in this case at a second end of the roller body 30 opposite to the first end. Alternatively, the driven parts 31, 32 may be arranged at intermediate positions along the roller body 30. The features described hereafter in relation to the first driven part 31 apply mutatis mutandis to the second driven part 32.

[0072] In this example, the first driven part 31 is detachably mounted to the roller body 30 at a first end thereof in the lateral direction L. Alternatively, the first driven part 31 may be integrally formed with or as a part of the roller body 30. The first driven part 31 is not necessarily positioned at the end of the roller body 30, but may alternatively be formed or positioned at an intermediate position along the length of the roller body 30 in the lateral direction L.

[0073] As shown in FIG. 2, each first driven part 31 of the plurality of rollers 3 has a first drive profile F1, F2, . . . , Fn that is different for each roller 3 of the plurality of rollers 3. Each second driven part 32 has a second drive profile G1, G2, . . . , Gn that is mirror symmetrical to the first drive profile F1, F2, . . . , Fn of the same roller 3, preferably about a mid-plane perpendicular to the axial direction A.

[0074] In particular, the first drive profile F1, F2, . . . , Fn of the plurality of rollers 3 tapers at a taper rate or a taper angle H1-Hn that is different for each roller 3. More in particular, the taper rate or the taper angle H1-Hn decreases for each subsequent roller 3 in the transport direction T. In this example, the first driven parts 31 of all rollers 3 except for the last roller 3 in the transport direction T are conical. The conical first driven parts 31 have different conicities. In particular, the conicity of the first driven parts 31 decreases with each subsequent roller 3 in the transport direction T.

[0075] The taper rate may also be expressed as a ratio between the largest diameter and the smallest diameter, or between the largest circumference and the smallest circumference, of the first driven part 31. Note that the largest diameter or the largest circumference is the same for all driven parts 31, 32. The smallest diameter or smallest circumference is progressively increased from the first roller 3 in the transport direction T towards the last roller 3 in the transport direction T.

[0076] In the example as shown, the decrease is linear, i.e. with equal decrease intervals between pairs of subsequent rollers 3. It is noted that the decrease may also be non-linear, or a combination of linear and non-linear, depending on the shrink characteristics of the continuous strip 9. If for example the continuous strip 9 tends to contract strongly in an upstream section of the shrink conveyor 1 and less strongly in a downstream section of said shrink conveyor 1, the first drive profiles F1, F2, . . . , Fn may be adjusted accordingly. The conicity, taper rate or taper angles H1, H2, . . . , Hn may be the same for the first driven parts 31 of two or more rollers 3. It is further noted that one or more rollers 3 may have a non-tapering or non-conical first drive profile F1, F2, . . . , Fn, i.e. cylindrical or straight cylindrical, such as the last roller 3 in the transport direction T. The shrink conveyor 1 may for example have two or more rollers 3 at the downstream end of the shrink conveyor 1 that have a cylindrical first driven part 31.

[0077] FIGS. 3 and 4 show cross sections of two rollers 3 in the first roller position PI and the fifth roller position P5, respectively. As clearly shown, the first drive profile F1 of the first driven part 31 of the roller 3 in the first roller position P1 (FIG. 3) tapers at a first taper rate or a first taper angle H1 in excess of five degrees, whereas the fifth drive profile F5 of the first driven part 31 of the roller 3 in the fifth roller position P5 (FIG. 4) tapers at a first taper rate or a fifth taper angle H5 equal to or less than five degrees.

[0078] In the examples as shown, the taper rate or taper angle H1, H5 is constant along the respective first drive profiles F1, F5, resulting in a linear first drive profile F1, F5. It is however envisioned that in an alternative embodiment, the taper rate or taper angle H1, H5 is not constant. The first drive profile H1, H5 may for example be non-linear, convex, concave and/or crowned.

[0079] In FIGS. 3 and 4, the first driven part 31 is shown as being integral with the roller body 30. Alternatively, the first driven part 31 may be separate part that is connected or fixed to said roller body 30. The first driven part 31 may also be detachable from the roller body 30 or exchangeable or interchangeable connected to said roller body 30, i.e. to modify the first drive profile F1-Fn of the respective roller 3 without replacing the entire roller 3.

[0080] As shown in FIG. 6, the shrink conveyor 1 further comprises a first drive member 41 and a second drive member 42 for contacting the first driven parts 31 and the second driven parts 32, respectively, of the plurality of rollers 3. The drive members 41, 42 extend in a direction parallel or substantially parallel to the transport direction T. The drive members 41, 42 are positioned underneath the rollers 3, i.e. along the roller positions P1, P2, . . . , Pn as defined by the frame 2. Alternatively, the drive members 41, 42 may be arranged above or around the rollers 3.

[0081] The drive members 41, 42 are configured for rotating the plurality of rollers 3 through said contact or friction with said first driven parts 31 and said second driven parts 32. In this example, the drive members 41, 42 are endless belts. The drive members 41, 42 are movable in the lateral direction L, as shown with arrows D, to adjust the contact position of said drive members 41, 42 relative to the driven parts 31, 32.

[0082] The drive members 41, 42 are mechanically coupled to move symmetrically in the lateral direction L. In particular, the shrink conveyor 1 comprises a displacement mechanism 5 for synchronously moving the drive members 41, 42 towards and away from each other in the lateral direction L. In this example, the displacement mechanism 5 comprises two spindle drives 51, 52 with oppositely threaded sections engaging with corresponding nuts 6 carrying the drive members 41, 42. The presence of two spindle drives 51, 52 ensure that drive members 41, 42 can remain mutually parallel and/or parallel to the transport direction T during their displacement in the lateral direction L.

[0083] Alternatively, the drive mechanism 5 may comprises linkages, tracks, gear racks or other suitable types of mechanical parts to displace the drive members 41, 42. In a further alternative embodiment, the drive members 41, 42 may be driven by individually controllable actuators, controlled to move synchronously, e.g. pneumatic, hydraulic or electric actuators.

[0084] Keeping the drive members 41, 42 parallel can further improve operator safety because of the reduced risk of pinching. Alternatively, the displacement mechanism 5 may be configured for introducing a slight skewing of the drive members 41, 42 towards and/or away from each other at one or both sides, to enhance the effect of the displacement on the speed of the rollers 3 towards one end of the shrink conveyor 1 in the transport direction T.

[0085] The shrink conveyor 1 further comprises one or more transport drives 53, 54, individually controllable and/or coupled to drive the drive members 41, 42 synchronously in the transport direction T.

[0086] As shown in FIGS. 3 and 4, the drive members 41, 42 are configured for contacting the rollers 3 in at least one contact position across the width of said drive members 41, 42. The rollers 3 rest on the drive members 41, 42 under the influence of gravity. In case of the conical driven parts 31, 32, the drive members 41, 42 may only contact the respective driven parts 31, 32 at the inside facing edge of said drive members 41, 42. In case of the cylindrical driven part 31, 32 at the last roller 3 in the transport direction T, the drive members 41, 42 may contact the respective driven parts 31, 32 across the entire width of said drive members 41, 42.

[0087] A method for allowing shrink in a continuous strip 9 with the use of the aforementioned shrink conveyor 1 will now be briefly elucidated with reference to FIGS. 1-6.

[0088] The method comprises the step of positioning the plurality of rollers 3 in an equal number of roller positions P1, P2, . . . , Pn of the plurality of roller positions P1, P2, . . . , Pn, in a regular pattern, as shown in FIGS. 1 and 2, or an irregular pattern, as shown in FIG. 5. The spacing between the rollers 3 may have an effect on the tendency of the continuous strip 9 to slack between subsequent rollers 3. More rollers 3 may be provided to prevent slack, or rollers 3 may be left out if slack is intended.

[0089] The method further comprises the step of driving the rollers 3 at different rotation speeds in accordance with the difference in taper rates or taper angles H1, H2, . . . , Hn between the respective drive profiles F1, F2, . . . , Fn, G1, G2, . . . , Gn. In particular, the rollers 3 are rotated at a rotation speed in a transmission ratio to the speed of the first drive member 41 that is defined by the diameter, the circumference or the circumferential length of the respective driven part 31, 32 at the contact position between the respective drive member 41, 42 and the respective driven part 31, 32 along the respective drive profile F1-Fn, G1-Gn. In the lateral positions of the drive members 41, 42 as shown in FIG. 2, the first roller 3 of the plurality of rollers 3 in the transport direction T has a relatively small circumference compared to the last roller 3 in the transport direction T, which has a constant or straight-cylindrical circumference. Hence, the speed of the first roller 3 is higher than the speed of the last roller 3 in the transport direction T. The rotation speeds of the rollers 3 between the first roller 3 and the last roller 3 will progressively decrease with each subsequent roller 3 in the transport direction T in accordance with the decreasing taper rate or taper angle H1, H2, . . . , Hn, depending on the relative position of the drive members 41, 42 with respect to the driven parts 31, 32 in the lateral direction L. The method further comprises the step of moving the first drive member 41 and the second drive member 42 in the lateral direction L to adjust the transmission ratio between the speed of the drive members 41, 42 and the rollers 3. As the drive members 41, 42 are kept mutually parallel and/or parallel to the transport direction T, all contact positions between the drive members 41, 42 and the respective driven parts 31, 32 are displaced in the lateral direction L along the respective drive profiles F1-Fn, G1-Gn with the same amount. The taper rate or taper angle H1, H2, . . . , Hn of the respective drive profiles F1-Fn, G1-Gn causes the roller 3 with the highest taper rate or taper angle H1 to change the most in speed, whereas for the roller 3 with the lower taper rate or taper angle Hn, the speed changes the least or remains constant.

[0090] The speed of the rollers 3 is determined by the relationship between the taper angle H1, H2, . . . , Hn and the speed at which the drive members 41, 42 are driven by the one or more transport drives 53, 54 in the transport direction T. The speed of the drive members 41, 42 can be adjusted to keep the speed of the first roller 31 in the transport direction T constant at all times. The taper angle H1, H2, . . . , Hn of the subsequent rollers 3 downstream of the first roller 3 then determines, in combination with the speed of the drive members 41, 42, the speed of the subsequent rollers 3 relative to said first roller 3.

[0091] For example, when the drive members 41, 42 contact the driven parts 31, 32 at a lateral position where all the driven parts 31, 32 have the same maximum diameter, the speed will be 100% across all rollers 3. However, when the drive members 41, 42 are moved laterally to a more outer position and the speed of the drive members 41, 42 is kept the same, the speed of the first roller 3 will increase the most, and the speeds of the subsequent rollers 3 in the transport direction T to an increasingly lesser extent. It is however preferred that first roller 3 is rotated at a constant speed, or at least a speed matching the speed of the pull off conveyor 8. Hence, the one or more transport drives 53, 54 can be controlled to reduce the speed of the drive members 41, 42 such that the speed of the first roller 3, despite the changed lateral position of the drive members 41, 42 relative to its drive profiles F1, G1, remains constant or substantially constant. The decreased speed of the drive members 41, 42 will cause an incremental decrease in speed across the subsequent rollers 3 in the transport direction T.

[0092] Note that the lateral position of the drive members 41, 42 relative to the rollers 3 can be controlled within a range defined by the width of the respective drive profiles F1-Fn, G1-Gn in said lateral direction L, which is the same for all driven parts 31, 32. This means that especially for rollers 3 with only a very small taper rate or taper angle, e.g. close to zero, the diameter difference between the endpoints of the respective drive profile F1-Fn, G1-Gn will be relatively small. Still, said relatively small diameter difference allows for a very accurate control of the speed or control with a very high resolution, by moving the drive members 41, 42 across the respective drive profile in the lateral direction L.

[0093] FIG. 7 shows an alternative shrink conveyor 101 according to a second embodiment of the invention, which differs from the aforementioned shrink conveyor 1 in that it features rollers 103 with driven parts 131, 132 that have drive profiles F101-Fn, G101, Gn that taper at a taper angle that increases which each subsequent roller 103 in the transport direction T. In particular, the drive parts 131, 132 have a minimum diameter that is the same for all drive parts 131, 132 and a maximum diameter that increases from the first roller 103 in the transport direction T towards the last roller 103 in the transport direction T. Hence, in contrast to the previously discussed embodiment, the first roller 103 is always driven at a constant ratio to the speed of the drive members 41, 42, whereas the speed of the subsequent rollers is increasingly dependent on the relationship between the speed of the drive members 41, 42 and the increasing taper angles. This can simplify the control of the drive members 41, 42, because their speeds do not have to be adjusted to keep the speed of the first roller 103 constant.

[0094] FIG. 8 shows a further alternative shrink conveyor 201 according to a third embodiment of the invention, which differs from the previously discussed embodiments in that it features rollers 203 which driven parts 231, 232 that have drive profiles F201-Fn, G201-Gn that taper at a constant taper angle. In other words, the taper angle is the same for all driven parts 231, 232. The variable speed difference is generated by skewing or rotating the drive members 241, 242 from a neutral orientation in which said drive members 241, 242 are parallel or substantially parallel to the transport direction T, into a skewed orientation in which said drive members 241, 242 are at an oblique angle to the transport direction T. The skewing allows for a variable contact position between the drive members 241, 242 in the lateral direction L for the range of rollers 203. In particular, the drive members 241, 242 can be skewed such that they contact the first roller 203 at or near the minimum diameter and the last roller 203 at or near the maximum diameter of the driven parts 231, 232.

[0095] FIG. 9 shows a further alternative shrink conveyor 301 according to a fourth embodiment of the invention, which differs from the first embodiment of the invention (FIGS. 1-6) in that it features rollers 303 that have second driven parts 332 which are not mirror-symmetrical to the first drive parts 31. Hence, the second drive profiles G301-Gn taper in the same direction as the first drive profiles F1-Fn. Consequently, the drive members 41, 42 can be moved in the same direction parallel to the lateral direction L, instead of towards and away from each other, thereby allowing for a simplification of the displacement mechanism (not shown).

[0096] It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the scope of the present invention.