US20020092883A1

US20020092883A1 - Part feeder

Info

Publication number: US20020092883A1
Application number: US10/024,830
Authority: US
Inventors: Joel Andersson
Original assignee: TEK PAK SCANDINAVIA AB
Current assignee: TEK PAK SCANDINAVIA AB
Priority date: 2001-01-05
Filing date: 2001-12-18
Publication date: 2002-07-18
Also published as: SE0100054D0

Abstract

A manually actuatable, part feeder presents at least one exposed part, with an appropriate orientation for picking and placing, to an operator in a pick station, in response to the operator providing a feed command. A cover take-up mechanism can be used to remove a cover tape from the carrier such that the operator receives the exposed part or parts to be picked. Tape advance is achieved by applying forces to the carrier tape to advance the pocketed component carrying portion. Variable widths of carriers can be accommodated in the feeder. A pair of movable hold-down rails, laterally adjustable with respect to one another, makes it possible to feed carriers having a wide range of widths simply by adjusting the spacing of the rails relative to one another.

Description

FIELD OF THE INVENTION

The invention pertains to equipment for feeding parts for assembly of product. More particular, the invention pertains to such part feeders which are suited for use in semi-automatic or manual, final assembly or manufacturing processes.

BACKGROUND OF THE INVENTION

Numerous types of products are assembled, in whole or in part, on substantially automated assembly lines without direct human intervention. Examples of these include electronic products and subassemblies thereof.

Carrier tape is a form of packaging used for different kinds of smaller components or parts. It is made of polystyrene and other polymers with different thicknesses between 0.15 mm and 0.50 mm and varies in width between 8 mm and 200 mm called flastock.

The flat stock is heated and formed in a thermoforming machine. The result is a pocketed tape with shaped pockets, specific for every component that is supposed to be packed. When the component or part is packed, the pocket is sealed with a cover film called cover tape thereby forming a two-part carrier tape. The advantage in using carrier tape compared to other packaging solutions is that the product reaches the customer in the same way it was packed, it will stay scratch and dust free. The product volume is also very high compared to competing solutions.

Known assembly machines often incorporate components carried in standardized carrier tape. The respective carrier tape usually includes the cover tape to retain the part properly within the carrier during shipment and assembly.

Known carrier tapes are intended to be loaded into automatic part feeding machinery. Known machines will, for example, unwind a loaded carrier tape, strip off the cover tape and automatically provide for the removal of parts one at a time from the respective carrier tape and to the appropriate location in the pick and place assembly machinery.

The tapes, if perforated with sprocket or index holes can be advanced with a sprocket mechanism. Alternately, a linearly moving tape advance mechanism can be used.

Equipment for feeding carrier tape already exists on the market. Known equipment feeds the carrier tape with two cogwheels that run in the sprocket holes in the carrier tape. The carrier tape is wound up on a separate roll that uses the same drive force as the forward feeding but uses a slip friction clutch because of the increasing diameter of tape wound on the roll when the carrier tape winds up.

Known equipment is made to present a component in a specific position with very close tolerances in automated production lines. The need for close tolerance leads to high investment costs. Such machinery, while well suited for high volume mass production wherein the necessary capital investment can be spread across a large number of products, is, for a variety of reasons, often unsuited for lower volume, lower speed semiautomated assembly lines which involve human operators.

The market today is evolving toward manual assembly production in low labor cost countries. But still the carrier tape, as packaging, is the preferred way to pack and ship the components.

There is no known available equipment to present the carrier tape packed components for a manual work situation. All existing equipment is relatively expensive; and, designed only for fully integrated automatic assembly line situations.

Lower speed manual or semi-automatic assembly lines often use carrier trays for the parts. While less efficient than carrier tapes, the trays are well suited to lower speed manual or semi-automatic assembly lines.

There continues to be a need for less expensive, carrier tape based part feeders which are usable in conjunction with human operators in semiautomatic, lower speed and lower volume production lines. Preferably, such part feeders could be implemented with relatively low technology apparatus suitable for installation and use by operators of relatively limited skill levels in relatively low technology-type manufacturing lines.

SUMMARY OF THE INVENTION

A semi-automatic part feeder in accordance with the invention can be used in manual, one-at-a-time processes for assembly or sub-assembly of electronic products. Typical products include cellular telephones, circuit boards, pagers and other products or sub-assemblies thereof, where manual assembly is to be used.

In accordance herewith, the present part feeder can present a part in a preformed pocket in an elongated carrier tape to a pick station. The part is presented to an operator in the correct orientation for extraction and insertion.

The operator can manually pick the part from the carrier tape, for example with a hand-held vacuum wand. The part can then manually be placed into a sub-assembly or assembly such as a cellular phone or a pager.

In accordance herewith, the part is presented not only with the correct orientation for extraction and insertion, but also in a way which facilitates same. For example, sufficient clearance is provided relative to the part to permit easy and convenient use of the and to pick and to insert the part into assembly.

A manually operated switch, for example a foot operated switch, can be used to index one part at a time, or a group of parts, to the pick station. Alternately, a hand crank can be used to advance the tape.

Parts are supplied on pre-loaded reels of carrier tape. The parts are retained in their molded pockets in the tape by an overlying cover tape.

In another aspect of the invention, the loaded carrier tape can be unwound from a rotatably mounted reel. A cover tape take-up mechanism can be used to peel back the cover tape such that the operator is presented with an uncovered part at the pick station. This part can readily be extracted from the carrier pocket using the vacuum wand. The socketed tape is oriented so that gravity holds the parts in their respective pockets even in the absence of the cover tape.

The cover tape take-up mechanism not only peels off the cover tape, it applies a feed force to the carrier tape. The applied feed force advances the next loaded pocket of the tape to the pick station. Thus, the component carrying pocketed portion of the tape is not advanced using some form of indexing mechanism. It is drawn forward by the take-up forces applied to the cover tape.

First and second rails or guides, at least one of which is laterally adjustable, can be used to hold-down the pocketed tape so that it remains adjacent to the pick station. Various widths of tape can be used with the feeder merely by adjusting the spacing between the hold-down rails. This configuration is unlike prior art automatic feeders which are dedicated width units.

The present feeder assembly is a very flexible apparatus capable of feeding parts off of tapes having widths in a range from 5 to 250 mm. Unloaded sections of pocketed tape can be dumped into a container for recycling.

Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a part feeder in accordance with the present invention; [0025]
FIG. 2 is an enlarged perspective view of a portion of the feeder illustrated in FIG. 1; [0026]
FIG. 3 is an enlarged perspective view of a portion of the feeder illustrated in FIG. 2; [0027]
FIG. 4 is a front elevational view of the feeder illustrated in FIG. 1; [0028]
FIG. 5 is an enlarged fragmentary front elevational view of a portion of FIG. 4; [0029]
FIG. 6 is another perspective view of the feeder of FIG. 1 illustrating various details in phantom; [0030]
FIG. 7 is a side elevational view of another part feeder in accordance with the invention; and [0031]
FIGS. 8A, B, C illustrate different views of a collapsible cover tape spindle usable with the feeder of the present invention. [0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While this invention is susceptible of embodiment in many different forms, there are shown in the drawing and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. [0033]
FIG. 1 illustrates a [0034] part feeder 10 in accordance with the presence of the present invention. Feeder 10 is supported on a support surface S. One or more feeders 10 can be positioned next to one another on surface S. Hence, a plurality of different parts can be presented to an operator simultaneously.
[0035] Feeder 10 includes a support frame or housing indicated generally at 12 which carries various portions of the feeder 10. A carrier tape support bracket and feed mechanism 14 is coupled to and carried on the frame 12. The support 14 rotatably supports a reel R of a loaded carrier tape T.
The reel R and tape T could carry a wide variety of parts and could have a structure in accordance with any of the recognized standards for part carriers or carrier tapes. It will be understood that the specific nature of the parts carried on the tape T is not a limitation of the present invention. [0036]
Tape T is preferably a two-part tape having a cover tape C and a pocketed section P. The cover tape C is adhesively attached to section P. [0037]
Section P includes a plurality of spaced apart pockets P[0038] 1, P2 . . . Pn. One or more components can be carried in each pocket Pi as would be understood by those of skill in the art.
Tape T is fed off of reel R by a feed mechanism indicated generally at [0039] 18. Feed mechanism 18 which is carried on frame 12 could for example include an electric motor 18-1 coupled by a gear train 18-21 (best seen in FIG. 6) to a take-up reel 18-3 for cover tape C.
As the motor [0040] 18-1 is energized by drive circuits 18-6 on printed circuit board 18-7 (also best seen in FIG. 6), the tape-up reel 18-3 is driven to rotate in a direction R1. As the take-up reel 18-3 rotates, it pulls cover tape C wrapped thereon off of, and away from, pocketed section P over roller 18-8, in a direction D1.
The force applied by take-up reel [0041] 18-3 also advances the tape T and pocketed section P in a direction D2. The advancing pockets Pi are oriented so as to use the force of gravity to retain the component(s) in the respective pocket(s). As the tape T advances in direction D2, it unwinds from reel R. The cover tape C is wound onto take-up reel 18-3 with a peel angle in a range of 25 to 40 degrees depending on the diameter of the roll of cover tape C on the take-up reel 18-3.
As the tape T is fed off of reel R by [0042] feed mechanism 18, the peripheral edges thereof E1, E2 slide under and are retained by rails 22 a and 22 b. The rails 22 a, 22 b are laterally movable relative to one another to enable feeder 10 to feed tapes of differing widths. Only one of the rails 22 a, needs to be adjustable relative to the other. Preferably, the rails are adjustable relative to one another to retain tapes having a width in a range of 5 mm to 250 mm.
The rails [0043] 22 a, b provide slots 24 a, b on the order of 1 mm through which the edges E1, E2 slide. The tape T enters the slots 24 a, b before the cover tape C is stripped from the section P.
Once the pocketed section P passes the cover tape take-up reel [0044] 18-3, it enters a pick area 32. The pick area 32 is defined by an enlarged open region 32 in cover 46 of housing 12. The respective carrier tape pocket, such as pocket Pi, is presented to an operator with an appropriate orientation and with enough clearance in the pick area 32 to facilitate easy extraction of the respective component or part from the pocket Pi.
The size of the [0045] pick region 32 can be altered by replacing cover 46 with a cover having a pick region of a desired size. Hence, various sizes of pockets can easily be compensated for. In addition, multiple pockets can be presented with a single tape motion in a single pick region if desired.
An operator, not shown, can use a [0046] vacuum wand 38 to pick the respective part, from the pocket Pi for transfer to an assembly or subassembly being manufactured. As each part is removed from the respective pocket, via wand 38, the operator indexes the advance mechanism 18 moving the next pocket Pi, and associated part, into the pick area 32.
The [0047] mechanism 18 can be triggered to advance the tape T one index position at a time using a foot switch 38 a or a hand switch 38 b. In an alternate embodiment, a crank or shaft can be coupled to the advance mechanism 18 to mechanically advance the tape T using non-electrical energy.
The amount of advance or pitch for each cycle can be set, based on the size of the pockets Pi, using [0048] switches 40 generally indicated in FIG. 6. A display 42 can be provided to indicate current pitch setting.
Feedback is provided by a sprocket wheel carried on printed [0049] circuit board 44. The sprocket wheel engages sprocket holes in section P and is advanced thereby. Once motor 18-1 has been energized, it will run until the section P has been advanced an appropriate number of sprocket or index holes.
It will be understood that the [0050] pick region 32 can be configured to expose two or more pockets Pi with each index cycle. An operator can thus pick and place multiple components or parts during each cycle. Conversion from one pick area to another is easily accomplished by replacing cover 46 which defines pick region 32.
Once the tape T has passed through [0051] pick region 32, it continues to be fed via the rails 22 a, 22 b and moves to a distal region of the feeder 10. The unloaded tape T can then be accumulated in a scrap or recyclable container for subsequent processing.
It will be understood that the [0052] feeder 10 is particularly advantageous in that as the tape T is feed into the pick region 32, with the cover tape removed, the orientation of the part is such that gravity continues to hold the part into the respective pocket Pi. At the same time, the part is readily available to the pick-up end of the wand 38 for the convenience of the operator. As noted above, the pick region 32 is designed to facilitate extraction by providing clearance for the operator to use the vacuum wand 38 to remove the parts. Alternatively, pick region 32 can be designed to permit manual extraction of parts by an operator.
Another advantage of the [0053] part feeder 10 is that it is a relatively low cost easy-to-use mechanism which is well-suited to semi-automatic assembly type manufacturing using personnel of limited skills where only modest capital investments in assembly equipment can be justified. Additionally, the relatively non-complex nature of the feeder 10 is very beneficial in that it can be maintained and kept operational by personnel of limited skills and with limited tools and parts.
FIG. 7 illustrates an [0054] alternate embodiment 10′ of a part feeder in accordance with the present invention. The same identification numerals have been used in FIG. 7, designated with a prime, as were used in FIGS. 1-6 for corresponding structures. As illustrated in FIG. 7, part feeder 10′ extracts tape T′ from reel R′ using an electric motor, such as electric motor 18-1′ to strip cover tape C′ from pocketed portion P′. The pocketed portion P′ is fed beneath cover 46′ to a pick region indicated generally at 32′ for the convenience of an operator.
In the [0055] part feeder 10′, housing 12′ incorporates a variable depth floor 12′-1 whose depth can be set using mechanism 12′-2 to compensate for various depths of pockets P′i in the pocketed portion P′. As illustrated in FIG. 7, tape T′ slides across proximal rounded bottom plate 12′-3 as it is being advanced by the motor 18-1′, stripping the cover tapes C′. Guide rails, comparable to guide rails 22 a, b; are provided in feeder 10′ beneath cover 46′. As discussed above, the tape T′ is advanced by electric motor 18-1′ stripping cover tape C′ and pulling it in a direction D1′ which in turn advances the pocketed portion P′ in a direction D2′ toward the pick region 32′. A printed circuit board comparable to printed circuit board 44 carried within housing 12′ provides similar functions described previously with respect to circuit board 44.
FIGS. [0056] 8A-C illustrate a cover tape take-up assembly 50. Assembly 50 is rotatable by motor or gear drive 52 as discussed previously to rotatably take up cover tape, such as cover tape C as in FIG. 1, so as to advance pocketed section P. Assembly 50 includes a rotatable, pivotably arranged spindle portion 54 a and a separable expander 54 b.
The cover tape C is wound onto rotatable [0057] elongated body elements 56 a, b (configured as in FIG. 8A) between disks 58 a, b, best seen in FIG. 8C. Body elements 56 a, b are pivotably attached, indicated generally at 60 a, b to a coupling shaft rotatable by motor or gear drive 52. The body elements are biased toward one another by an elastic member, such as O-ring 60. In the configuration of FIG. 8B, elements 56 a, b exhibit a tapered external periphery.
When expander [0058] 54 b is slidably engaged with spindle portion 54 a, the biasing forces are overcome and body elements 56 a, b are forced to rotate away from one another thereby forming a generally cylindrical take-up reel of a substantially constant radius, best seen in FIG. 8A. When expander 54 b is withdrawn from assembly 54 a, the free ends 56 a′, b′move laterally toward one another, see FIG. 8B, and resume a tapered state.
When a reel of removed cover tape C has been accumulated on [0059] assembly 50, expander 58 b can be removed therefrom. The reel of cover tape C can be slid from the tapered exterior periphery of elements 56 a, b. The reel of cover tape C can be cut loose and removed.
Expansion element[0060] 58 b can be reinserted axially between elements 56 a, b. The free end of cover tape C extending around cylinder 18-8 can be reattached to spindle 54 a. Part feeding and assembly can continue.
It will be understood that while two pivotably attached [0061] elements 56 a, b have been illustrated, three or four could be used. The number of such elements is not a limitation of the invention. As illustrated in FIG. 8C, the cover tape C, pealed off of pocketed portion P can be rolled onto the take-up reel in either direction R1, see FIG. 2, or direction R2. The exact details of take-up direction are not a limitation of the invention.
From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims. [0062]

Claims

What is claimed:

1. A part feeder comprising:

a support for an elongated, pocketed, product carrier with a removable elongated cover;

a mechanism for moving the carrier a predetermined distance in response to a manually generated input by applying a separating force to the cover;

a work station upon which a portion of the carrier can be supported for manual removal of a part carried therein wherein the product carrier is supported with an orientation that tends to retain the part in a respective pocket until manually removed.

2. A feeder as in claim 1 wherein the support comprises a mount for rotatably supporting a reel of tape.

3. A feeder as in claim 1 wherein the mechanism comprises a cylindrical tape take-up member rotated by an electrically driven transducer.

4. A feeder as in claim 3 wherein transducer is an electric motor.

5. A feeder as in claim 1 which includes a cover tape take-up mechanism positioned adjacent to the work station.

6. A feeder as in claim 1 which includes at least one, elongated carrier guide element.

7. A feeder as in claim 6 which includes a second guide element, and, wherein at least one of the guide elements is movable laterally relative to the other.

8. A feeder as in claim 1 which includes a manually operated control switch, coupled to the mechanism, for generating the control signal.

9. A feeder as in claim 7 wherein the guide elements are movable, relative to one another for use with carriers having a width parameter in a range of at least 5 mm to 250 mm.

10. A feeder as in claim 1 wherein the carrier is at least in part covered at the work station.

11. A feeder as in claim 1 wherein the mechanism winds up the cover.

12. A feeder as in claim 11 wherein the mechanism includes a roller for substantially reversing a direction of travel of the cover tape.

13. A feeder as in claim 1 which includes a carrier retaining member which extends, at least in part, to a product removing location.

14. A feeder as in claim 13 which includes a tape guide member, displaced from the carrier retaining member wherein the pocketed product carrier advances therebetween.

15. A carrier tape feed mechanism comprising:

support for a tape to be fed;

a mechanism for separating a tape being fed into a free cover tape and a pocketed component carrying tape;

a tape advance apparatus which engages at least apart of the free cover tape and which applies a feeding force thereto thereby advancing the pocketed tape a predetermined amount with the pocketed tape oriented to retain the components in respective pockets.

16. A mechanism as in claim 15 wherein the support rotatably supports a reel of carrier tape.

17. A mechanism as in claim 15 which includes a picking station for the pocketed tape.

18. A mechanism as in claim 15 wherein the tape advance apparatus includes a cover tape take-up device.

19. A mechanism as in claim 18 wherein the cover tape take-up device comprises a take-up reel.

20. A mechanism as in claim 15 which includes at least one guide for use with variable widths of carrier tape.

21. A mechanism as in claim 20 wherein the guide includes a width adjusting, laterally movable guide section.

22. A mechanism as in claim 20 wherein the guide comprises a fixed section and second section movable with respect to the fixed section.

23. A mechanism as in claim 15 wherein the tape advance apparatus includes an electrically energized actuator for generating the feeding force.

24. A mechanism as in claim 23 wherein the actuator comprises at least one of an electric motor and a solenoid.

25. A mechanism as in claim 23 which includes a manually activatable control member for intermittently applying the feeding force.

26. A part presenting unit comprising:

a support structure;

a reel element, carried by the support structure for rotatably carrying a reel of a pre-loaded carrier tape;

a picking station, carried by the support structure;

a tape advance mechanism, carried by the support structure, wherein the mechanism separates a carrier tape from the reel into a cover portion; and a component carrying tape and wherein the tape advance mechanism includes a transducer for applying an advancing force to the cover portion whereby the component carrying tape is advanced to the picking station, wherein the station has a region for providing manual access to a selected section of the component carrying portion.

27. A unit as in claim 26 wherein:

the transducer comprises an electric motor to sequentially present successive regions of the component carrying tape at the picking station.

28. A unit as in claim 26 wherein the picking station includes a cover with an access port having an operator surface and a component carrying tape surface with a tape guide located adjacent to the component carrying tape surface wherein the component carrying tape is interposed between the cover and the guide as it is being advanced to the picking station.

29. A unit as in claim 28 wherein the tape advance mechanism reverses, at least in part, a direction of movement of the cover tape.

30. A tape feed mechanism for a two part carrier tape wherein one part corresponds to a pocketed tape with a second part that corresponds to a cover tape, the mechanism comprising:

a pocket access station wherein the station has a tape input port and a tape output port; a cover tape separating station adjacent to the input port wherein a cover tape is separated from a pocketed tape;

an actuator for applying a force to the cover tape, separating same from the pocketed tape and advancing same toward the tape output port wherein the tape access station orients the tape to prevent components carried by the pocketed tape from falling from the respective pocket, as the carrier tape is removed.

31. A mechanism as in claim 30 which includes at least one elongated tape guide extending from the separating station.

32. A mechanism as in claim 31 which includes a second elongated tape guide wherein one guide is movable relative to the other.

33. A mechanism as in clam 30 wherein the actuator is selected from a class which includes a manually activated actuator and an electrically activated actuator.

34. A mechanism as in claim 33 wherein the manually activated actuator includes a manually movable member for applying the force to the cover tape.

35. A mechanism as in claim 33 wherein the electrically activated actuator comprises one of a motor and a solenoid.

36. A mechanism as in claim 30 which includes an elongated, covered pocketed tape receiving region which extends between the ports.

37. A mechanism as in claim 36 wherein the covered region includes a part removal port.

38. A mechanism as in claim 37 wherein the actuator intermittently applies force to the cover tape to sequentially advance pockets in the pocketed tape to the part removal port.

39. A mechanism as in claim 38 which includes a cover tape take-up reel.

40. A mechanism as in claim 39 wherein the actuator intermittently rotates the take-up reel.

41. A method of presenting parts pre-packaged in a reel of flexible carrier tape which has a cover tape which is attached to a pocketed tape, the method comprising:

unwinding a portion of the carrier tape with an orientation such that gravity retains the respective parts in the carrier tape;

applying a force to a cover tape thereby stripping the cover tape from a pocketed tape while at the same time moving a selected part to a predetermined location, in response to the force while restraining the part in a respective pocket of the pocketed tape.

42. A method as in claim 41 which includes:

manually removing the selected part and repeating the above steps.

43. A method as in claim 41 which includes moving the stripped cover tape in a direction, at least in part, opposite a direction of movement of the pocketed tape.

44. A method as in claim 41 which includes counting tape based indicia to determine how far to move the pocketed tape.

45. A method as in claim 41 which includes guiding the pocketed tape using at least one guide slot.

46. A method as in clam 41 which includes orienting the pocketed tape so that gravity restrains the part in the respective pocket in the absence of the cover tape.

47. A part feeder system comprising:

a base;

a plurality of separate part feeders couplable to the base wherein each member of the plurality includes an adjustable width, pocketed tape advance and pick structure settable for an expected tape width and adjustable pocket spacing along the tape wherein the structure carries a replaceable pick-region defining cover wherein at least one component carrying pocket in the tape is presented for manual picking at the pick-region wherein the respective pocket extends away from the cover; and

a tape advance mechanism, carried on the structure, with at least one cover tape take-up roller configured, relative to the settable width of the structure, to strip a cover tape from a section of pocketed tape and roll the cover tape onto the take-up roller while at the same time linearly advancing the coverless section of pocket tape toward the pick-region with the cover blocking access to components to be picked in pockets of the section of tape except as the respective pockets enter the pick region.

48. A system as in claim 47 wherein the pockets each include a closed end region against which the respective component carried therein is drawn by the force of gravity, at least in the pick region.

49. A system as in claim 47 wherein the cover tape take-up roller comprises a removable outer hub for removing a reel of cover tape wound on the roller.

50. A system as in claim 47 wherein the cover tape take-up roller comprises an alterable central section having a first, tape winding state and a second, wound tape removal state.

51. A system as in claim 50 wherein the central section comprises pivotably mounted elongated members which exhibit a cylindrical profile in the first state and a non-cylindrical profile in the second state.

52. A system as in claim 51 which includes an axially slidable member for converting the central section from one state to the other.

53. A system as in claim 3 wherein the take-up member comprises a removable outer hub for removing a reel of cover tape wound on the roller.

54. A system as in claim 3 wherein the take-up member comprises an alterable central section having a first, tape winding, state and a second, wound tape removal state.

55. A system as in claim 54 wherein the central section comprises pivotably mounted elongated members which exhibit a cylindrical profile in the first state and a non-cylindrical profile in the second state.

56. A system as in claim 55 which includes an axially slidable member for converting the central section from one state to the other.