Idler Roller Actuating Device

Abstract

An idler roller actuating device for a conveyor having a conveyor frame, an idler roller having a roller frame pivotable on the conveyor frame, and a belt passing over the idler roller and having a normal operating position is disclosed. The idler roller actuating device is disposed adjacent one side of the belt and has a pivot member pivotable on the conveyor frame; a sensing arm affixed to the pivot member had having a sensing arm free end; a sensing member mounted on the sensing arm free end of the sensing arm adjacent the one side of the belt; a first tension member affixed to the pivot member and having a first tension member free end; and a second tension member affixed to the roller frame and having a second tension member free end pivotably connected to the first tension member free end. The sensing member is engageable with the one side of the belt when the belt moves away from the normal operating position and toward the one side of the belt to rotate the sensing member and the sensing arm in one direction of a counterclockwise direction and a clockwise direction. The first tension member and the second tension member are operable by the rotation of the sensing member and the sensing arm to rotate the roller frame and the idler roller in the other direction of the counterclockwise direction and the clockwise direction so that the idler roller reverses the movement of the belt away from the normal operating position and returns the belt to the normal operating position.

Description

BACKGROUND OF THE INVENTION

Heretofore, conventional conveyors and more particularly conventional troughing conveyors and the like, employed to transfer dry comminuted material, such as limestone, iron ore and the like have had several disadvantages and defects. Such conveyors are adjusted or trained on their head roller, tail roller, and idler rollers while they are empty. After several weeks of load carrying operation, the head roller or the tail roller or the conveyor frame may shift from its original trained position, thus producing a shift of the conveyor belt to one side of the idler rollers with resultant riding off of the belt over such idler rollers. Similarly, an improper belt splice (where the two spliced edges are not parallel to each other) may produce the same undesirable result. Further, since the conveyed load is often loaded from one side of the conveyor belt, the piling up of the load on the other side will also cause a shift in the conveyor belt from its normal operating position, for example, where the longitudinal centerline of the conveyor belt is aligned with the centerline of the idler rollers toward such one side. Again, the characteristics of the conveyor may change, such as by elongation or contraction of either the load carrying or nonload carrying surface thereof or the deposition of a fluid, such as water or the like, on one surface thereof, or the like, to produce such undesirable transverse shift of the belt.

Conventional devices are available for restraining such undesirable transverse movement of the conveyor belt during a load carrying operation, but none are available for sensing the above-described undesirable transverse movement and then actuating the idler roller to move the conveyor belt back to its normal operating position.

OBJECTS OF THE INVENTION

It is the general object of this invention to avoid and overcome the foregoing and other difficulties of and objections to prior art practices by the provision of an improved idler roller actuating device which:

a. senses the undesirable transverse movement of a conveyor belt and then actuates the associated idler roller to return the conveyor belt to its normal operating position;

b. is simple and rugged in structure;

c. has a long maintenance free operational life;

d. is readily repaired with a minimum of conveyor down time; and

e. has a minimum number of moving or wearing parts.

BRIEF SUMMARY OF THE INVENTION

The aforesaid objects of this invention, and other objects which will become apparent as the description proceeds, are achieved by providing an idler roller actuating device for a conveyor having a conveyor frame, an idler roller having a roller frame pivotable on the conveyor frame, and a belt passing over the idler roller and having a normal operating position. The idler roller actuating device is disposed adjacent one side of the belt and has a pivot member pivotable on the conveyor frame; a sensing arm affixed to the pivot member and having a sensing arm free end; a sensing member mounted on the sensing arm free end of the sensing arm adjacent the one side of the belt; a first tension member affixed to the pivot member and having a first tension member free end; and a second tension member affixed to the roller frame and having a second tension member free end pivotably connected to the first tension member free end. The sensing member is engageable with the one side of the belt when the belt moves away from the normal operating position and toward the one side of the belt to rotate the sensing member and the sensing arm in one direction of a counterclockwise direction and a clockwise direction. The first tension member and the second tension member are operably by the rotation of the sensing member and the sensing arm to rotate the roller frame and the idler roller in the other direction of the counterclockwise direction and the clockwise direction so that the idler roller reverses the movement of the belt away from the normal operating position and returns the belt to the normal operating position.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of this invention, reference should be had to the accompanying drawings, wherein like numerals of reference indicate similar parts throughout the several views and wherein:

FIG. 1 is a fragmentary plan view of a portion of a conveyor, one of its idler rollers and the improved idler roller actuating device, and showing the sensing members normally in engagement with the edges of the belt and the centerline of the belt moved to the left of the centerline of the conveyor,

FIG. 2 is a view similar to an end elevational view of the apparatus shown in FIG. 1, taken along the line 2-2 of FIG. 1 in the direction of the arrows,

FIG. 3 is a side elevational view of the apparatus shown in FIG. 1, taken along the line 3-3 of FIG. 1 in the direction of the arrows,

FIG. 4 is a fragmentary plan view of an alternative embodiment, showing a fixed sensing member mounted on the free end of the sensing arm,

FIG. 5 is a view similar to FIG. 4 showing a fixed rigid or resilient shoe utilized as the sensing member,

FIG. 6 is a view similar to FIGS. 4, 5, showing a pivotable rigid or resilient shoe as the sensing member,

FIG. 7 is a fragmentary plan view of an alternative embodiment of the first tension member and the second tension member showing a positionable first tension member,

FIG. 8 is a view similar to FIG. 7 showing a spring as the second tension member,

FIG. 9 is a view similar to FIGS. 7, 8 showing an apertured bar or angle as the first tension member and a threaded rod with a connector on each end as the second tension member,

FIG. 10 is a fragmentary plan view of a connection member having a positioning slot and a pivot block secured in the slot in the desired location,

FIG. 11 is a fragmentary plan view of a fixed sleeve secured to the conveyor frame, as by welding or the like, and a post or shaft pivotable in such fixed sleeve with the sensing arm and first tension member removed for clarity,

FIG. 12 is a view similar to FIG. 11 showing a fixed post secured to the conveyor frame and a pivotable sleeve about the fixed shaft or post,

FIG. 13 is a side elevational view of a return idler roller showing the improved idler roller actuating device in the operating position,

FIG. 14 is a plan view of an alternative embodiment showing the sensing arm mounted on the first tension member, which first tension member is secured to a rotatable sleeve pivotable on a fixed shaft upstanding from the conveyor frame,

FIG. 15 is a view similar to FIG. 14 of another alternative embodiment showing the first tension member mounted on the sensing member and the sensing member secured to a rotatable shaft pivotable on a bearing secured to the conveyor frame, and

FIG. 16 is a view similar to FIG. 2 showing the sensing members normally spaced from the edges of the belt.

Although the principles of this invention are broadly applicable to conveyors, this invention is particularly adapted for use in conjunction with a troughing conveyor and hence it has been so illustrated and will be so described.

DETAILED DESCRIPTION

With specific reference to the form of this invention illustrated in the drawings, and referring particularly to FIGS. 1--3, a conveyor for transporting material, such as crushed limestone and the like, is indicated generally by the reference numeral 10.

This conveyor 10 has a conveyor frame 12 (FIGS. 1--3), an idler roller 14 (FIGS. 1--3) having a roller frame 16 (FIGS. 1--3) pivotable on a shaft 17 in a bearing 18 (FIG 2) mounted on the conveyor frame 12. A belt 20 (FIGS. 1--3) passes over the idler roller 14 and has a normal operating position. This normal operating position has the belt centerline B-B (FIG. 1) disposed in alignment with the idler roller centerline A-A (FIG. 1). The idler roller 14 has central roller 14a and outer rollers 14b (FIGS. 1, 2) mounted on shafts 14c journaled in brackets 14d upstanding from the roller frame 16.

Idler roller actuating devices 22a, 22b (FIGS. 1--3) are disposed on each side of the belt 20 for the purpose of sensing deviation of the belt 20 from its normal operating position, for example, to the left to the position shown in FIG. 1. Since the idler roller actuating devices 22a, 22b are similar, it is deemed sufficient to described idler roller actuating device 22a.

IDLER ROLLER ACTUATING DEVICE 22a

The idler roller actuating device 22a has a pivot member or sleeve 24 (FIGS. 1--3) pivotable on a post 26 (FIGS. 1--3) upstanding from the free end of a support member 28 (FIGS. 1--3) affixed to the conveyor frame 12 at 30, as by a bolt and nut or the like (FIGS. 1--2). A sensing arm 32 (FIGS. 1--3) is affixed at 34, as by a screw or the like (FIG. 2), to the upper portion of the pivot sleeve 24 (FIG. 2) and has a sensing arm free end 36 (FIGS. 1--3). A sensing member 38 (FIGS. 1--3), such as a roller or the like, is pivotable at 40 (FIGS. 1--2) on the free end 36 of the sensing arm 32. When the belt 20 is in the normal operating position, the sensing arm is disposed at the angle a (FIG. 1) equal to about 15.degree.--20.degree..

A first tension member or arm 42 (FIGS. 1--3) is mounted at 44 (FIG. 2) as by a screw or the like, on lower portion of the pivot sleeve 24 (FIGS. 2--3) and has a first tension member free end 46 (FIGS. 1--2). A second tension member 48 (FIGS. 1--3) is secured at 50 (FIG. 1), as by a bolt and nut or the like, through one of the holes 52 (FIG. 1) in a connection member or plate 54 affixed to the roller frame 16. The connection point 50 is a distance d (FIG. 1) from the centerline A-A (FIG. 1) of the idler roller 14 or the conveyor frame 12. As the distance d is increased, the angle of rotation b (FIG. 1) of the idler roller 14 is decreased. The second tension member 48 has a free end 56 (FIG. 1) which is secured at 57, as by a pin or the like (FIG. 1) to the free end 46 of the first tension member 42. Stops 43 (FIGS. 1--3) are upstanding from the conveyor frame 12 to limit the rotation b of the idler roller 14.

OPERATION

When the sensing member 38 is engaged by one side or edge, for example the left side or edge, (FIG. 16) of the belt 20 or is continually in engagement with such left side (FIG. 1) of the belt 20 and the belt 20 moves to the left, to the position shown in FIG. 1, the sensing member 30 is moved away from the normal operating position (not shown) to the position shown in FIG. 1 where the belt centerline B-B is a distance d.sub.1 (FIG. 1) from the idler roller centerline A-A. The sensing member 38 has also moved a distance d normal to its point of contact 58 (FIG. 1) with the belt 12. However, the sensing roller 38 has also moved on an arc greater than the distance d to the position shown in FIG. 1 where the angle a is now about 40.degree. to 50.degree.. The sensing roller 38 is moved in one direction of a clockwise direction and a counterclockwise direction (in this case a counterclockwise direction as shown by the arrow in FIG. 1).

The first tension member 42 and the second tension member 48 are operable (in the same counterclockwise direction) by the rotation of the sensing roller 38 and the sensing arm 32 to rotate the roller frame 16 and the idler roller 14 in the other direction of such clockwise direction and counterclockwise direction (i.e. clockwise direction) as shown by the arrow in FIG. 1, so that the idler roller 14 reverses the leftward movement (FIG. 1) of the belt 20 away from the normal operating position and returns the belt 20 to the normal operating position.

It will be noted from FIG. 1 that the angular increase in angle a from about 15.degree.--20.degree. to about 40.degree.--50.degree. by the leftward belt movement (FIG. 1) moves the idler roller 14 through the angle b of about 15.degree.--20.degree..

ALTERNATIVE EMBODIMENTS

It will be understood by those skilled in the art that alternatively the movable sensing roller 38 (FIGS. 1--3) may be replaced by a fixed sensing member (FIG. 6) or roller 38.sup.4 secured to the free end 36 of the sensing arm as by a bolt 60 and nut 62 or the like.

In FIG. 5 a fixed resilient or rigid shoe 38.sup.5 is affixed, as by welding, at 64 to the free end 36 of the sensing arm 32. The shoe 38.sup.6 (FIG. 6) may also be pivoted at 66 on the free end 36 by an arm 68, restrained in its movement by stops 70 on the free end 36 and biased by a spring 72 extending between a post 74 on the arm 68 to a post 74 on the free end 36.

In FIG. 1, the second tension member 48.sup.7 is a positionable turnbuckle or the like. FIG. 7 shows the first tension member 42.sup.7 as a positionable turnbuckle or the like and the second tension member as a fixed length arm 48.sup.7.

Referring to FIG. 8, the second tension member is a spring 48.sup.8 extending between a post 78 on the free end 46 of the first tension member 42 and a post 78 disposed in a selected hole 52 of the connection member 54.

The first tension member in FIG. 9 is a strap member, such as a bar or angle 42.sup.9 having spaced holes 80 therein. The second tension member (FIG. 9) is a threaded rod 48.sup.9 having threaded connectors 84 on each end thereof, which connectors 84 are connected at 57 to the free end 46 of the first tension member 42.sup.9 and to the connection member 54 at 50.

In FIG. 10 the connection member 54.sup.10 has a positioning slot 86 and a pivot block 88 secured, as by a nut 90 and a bolt 92 or the like, to the desired location in the slot 86. The second tension member, a fixed length arm 48.sup.10, is pivotable at 50 on the block 88.

FIG. 11 shows a portion of the conveyor frame 12 having a plate 94 mounted on two channels 96. A fixed sleeve or closed end pipe 24.sup.11 is secured to the conveyor frame 12 as by welds 98 or the like. The shaft or post 26.sup.11 rotates in the fixed sleeve 24.sup.11.

FIG. 12 has a fixed post 26.sup.12 (secured as by welds 98 or the like to) and upstanding from the conveyor frame 12 and a rotatable sleeve 24.sup.12 disposed about the fixed post 26.sup.12.

In FIGS. 1--3, the idler roller 14 has a central portion 14a and outer portions 14b which outer portions 14b are inclined at an angle c (FIG. 2) of about 20.degree.--35.degree. with respect to the central portion 14b. It will be understood that the outer portions 14b may be a straight line continuation of the central portion 14a or replaced by a single straight return roller 14.sup.13 as shown in FIG. 13.

FIG. 13 shows the improved idler roller actuating devices 22a, 22b in the upside-down position adjacent to the return roller 14.sup.13.

FIG. 14 shows a sensing mounting member 100 having sensing arms 102a, 102b between which the sensing roller 38.sup.14 is pivotably mounted at 40. The first tension member 42.sup.14 is secured (as by welds 98 or the like) to a rotatable sleeve 24.sup.14 which rotates on a fixed shaft 26.sup.14. The shaft 26.sup.14 is secured as by welds 104 to the conveyor frame 12. Alternatively, the sensing roller 38.sup.14 can be mounted at 40 on only one of the sensing arms 102a, or 102b, similar to the mounting shown in FIG. 1.

In FIG. 15 the sensing arm 32.sup.15 is secured as by welds 106 or the like to a shaft 26.sup.15 rotatable in a bearing 108 affixed to the conveyor frame 12 as by welds 106 or the like. A mounting member 100.sup.15 depends from the sensing arm 32.sup.15 and carries the first tension member 42.sup.15. A chain 110 is the second tension member and is secured by S-hooks 112 or the like at 57 and 50 to the free end 36.sup.15 of the first tension member 42.sup.15 and to a selected hole 52 in the connection member 54 respectively.

FIG. 16 shows the sensing members 38.sup.16 spaced a predetermined distance d.sub.2 from the edges of the belt 20.

SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION

It will be recognized by those skilled in the art that the objects of this invention have been achieved by providing improved idler roller actuating devices 22a, 22b which sense any undesirable transverse movement of the conveyor belt 20 from a normal operating position and then actuate the associated idler roller 14 to return the conveyor belt 20 to its normal operating position; is simple and rugged in structure; has a long maintenance free operational life; is readily repaired with a minimum of conveyor down time; and has a minimum number of moving or wearing parts.

While in accordance with the patent statutes preferred and alternative embodiments of this invention have been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.

Claims

I claim:

1. For a conveyor having a conveyor frame, an idler roller having a roller frame pivotable on said conveyor frame, and a belt passing over said idler roller and having a normal operating position, an idler roller actuating device disposed adjacent one side of said belt and having:

a. a pivot member pivotable on said conveyor frame;

b. a sensing arm affixed to said pivot member and having a sensing arm free end;

c. a sensing member mounted on said sensing arm free end adjacent said one side of said belt;

d. a first tension member affixed to said pivot member and having a first tension member free end; and

e. a second tension member affixed to said roller frame and having a second tension member free end pivotably connected to said first tension member free end;

f. said sensing member being engageable with said one side of said belt when said belt moves away from said normal operating position and toward said one side of said belt to rotate said sensing member and said sensing arm in one direction of a counterclockwise direction and a clockwise direction; and

g. said first tension member and said second tension member being operable by said rotation of said sensing member and said sensing arm to rotate said roller frame and said idler roller in the other direction of said counterclockwise direction and said clockwise direction so that said idler roller reverses said movement of said belt away from said normal operating position and returns said belt to said normal operating position.

2. The idler roller actuating device recited in claim 1 and having a support member affixed to said conveyor frame and said pivot member pivotable on said support member.

3. The idler roller actuating device recited in claim 1 wherein said roller frame has an idler roller centerline, said belt has a belt centerline and said normal operating position has said belt centerline disposed in alignment with said idler roller centerline.

4. The idler roller actuating device recited in claim 1 wherein said sensing member is a movable member.

5. The idler roller actuating device recited in claim 1 wherein said sensing member is a fixed member.

6. The idler roller actuating device recited in claim 1 wherein said sensing member is a shoe.

7. The idler roller actuating device recited in claim 1 wherein said sensing member is spaced from said belt when said belt is in said normal operating position.

8. The idler roller actuating device recited in claim 1 wherein said sensing member engages said belt when said belt is in said normal operating position.

9. The idler roller actuating device recited in claim 1 wherein said one direction is clockwise.

10. The idler roller actuating device recited in claim 1 wherein said one direction is counterclockwise.

11. The idler roller actuating device recited in claim 1 wherein said first tension member is positionable.

12. The idler roller actuating device recited in claim 1 wherein said second tension member is positionable.

13. The idler roller actuating device recited in claim 11 wherein said positionable first tension member is a turnbuckle.

14. The idler roller actuating device recited in claim 11 wherein said positionable first tension member is an apertured strip member.

15. The idler roller actuating device recited in claim 11 wherein said positionable first tension member is a threaded rod having a connector on each end thereof.

16. The idler roller actuating device recited in claim 11 wherein said positionable first tension member is a spring.

17. The idler roller actuating device recited in claim 12 wherein said positionable second tension member is a turnbuckle.

18. The idler roller actuating device recited in claim 12 wherein said positionable second tension member is a spring.

19. The idler roller actuating device recited in claim 12 wherein said positionable second tension member is an apertured strip member.

20. The idler roller actuating device recited in claim 12 wherein said positionable second tension member is a threaded rod having a connector on each end thereof.

21. The idler roller actuating device recited in claim 1 wherein said roller frame has a connection member, and said second tension member is connected to said connection member.

22. The idler roller actuating device recited in claim 21 wherein said connection member is provided with a plurality of apertures for connection of said second tension member thereto.

23. The idler roller actuating device recited in claim 21 wherein said connection member is provided with a slot and has a connector block affixed to said connection member for connection of said second tension member thereto.

24. The idler roller actuating device recited in claim 1 wherein said idler roller has a central portion and an outer troughing portion inclined at an angle to said central portion.

25. The idler roller actuating device recited in claim 1 wherein said idler roller has a central portion and an outer portion which is a substantially straight line continuation of said central portion.

26. The idler roller actuating device recited in claim 1 wherein said pivot member has a post member affixed to said conveyor frame and a sleeve member pivotable on said post member.

27. The idler roller actuating device recited in claim 1 wherein said pivot member has a sleeve member affixed to said conveyor frame and a post member pivotable in said sleeve member.

28. In combination:

a. a conveyor having a conveyor frame, an idler roller having a roller frame pivotable on said conveyor frame, and a belt passing over said idler and having a normal operating position, and

b. an idler roller actuating device disposed adjacent one side of said belt and having:

1. a pivot member pivotable on said conveyor frame;

2. a sensing arm affixed to said pivot member and having a sensing arm free end;

3. a sensing member mounted on said sensing arm free end adjacent said one side of said belt;

4. a first tension member affixed to said pivot member and having a first tension member free end; and

5. a second tension member affixed to said roller frame and having a second tension member free end pivotably connected to said first tension member free end;

6. said sensing member being engageable with said one side of said belt when said belt moves away from said normal operating position and toward said one side of said belt to rotate said sensing member and said sensing arm in one direction of a counterclockwise direction and a clockwise direction; and

7. said first tension member and said second tension member being operable by said rotation of said sensing member and said sensing arm to rotate said roller frame and said idler roller in the other direction of said counterclockwise direction and said clockwise direction so that said idler roller reverses said movement of said belt away from said normal operating position and returns said belt to said normal operating position.

29. For a conveyor having a conveyor frame, an idler roller having a roller frame pivotable on said conveyor frame, and a belt passing over said idler roller and having a normal operating position,

a. a first idler roller actuating device disposed adjacent one side of said belt,

b. a second idler roller actuating device disposed adjacent the other side of said belt,

c. each of said first idler roller actuating device and said second roller actuating device having:

1. a pivot member pivotable on said conveyor frame;

2. a sensing arm affixed to said pivot member and having a sensing arm free end;

3. a sensing member mounted on said sensing arm free end adjacent said one side of said belt;

4. a first tension member affixed to said pivot member and having a first tension member free end; and

5. a second tension member affixed to said roller frame and having a second tension member free end pivotably connected to said first tension member free end;

6. said sensing member being engageable with said one side of said belt when said belt moves away from said normal operating position and toward said one side of said belt to rotate said sensing member and said sensing arm in one direction of a counter clockwise direction and a clockwise direction; and

7. said first tension member and said second tension member being operable by said rotation of said sensing member and said sensing arm to rotate said roller frame and said idler roller in the other direction of said counterclockwise direction and said clockwise direction so that said idler roller reverses said movement of said belt away from said normal operating position and returns said belt to said normal operating position.

30. In combination:

a. a conveyor having a conveyor frame, an idler roller having a roller frame pivotable on said conveyor frame, and a belt passing over said idler roller and having a normal operating position,

b. a first idler roller actuating device disposed adjacent one side of said belt, and

c. a second idler roller actuating device disposed adjacent the other side of said belt,

d. each of said first idler roller actuating device and said second idler roller actuating device having:

1. a pivot member pivotable on said conveyor frame;

2. a sensing arm affixed to said pivot member and having a sensing arm free end;

3. a sensing member mounted on said sensing arm free end adjacent said one side of said belt;

4. a first tension member affixed to said pivot member and having a first tension member free end;

5. a second tension member affixed to said roller frame and having a second tension member free end pivotably connected to said first tension member free end;

6. said sensing member being engageable with said one side of said belt when said belt moves away from said normal operating position and toward said one side of said belt to rotate said sensing member and said sensing arm in one direction of a counterclockwise direction and a clockwise direction; and

7. said first tension member and said second tension member being operable by said rotation of said sensing member and said sensing arm to rotate said roller frame and said idler roller in the other direction of said counterclockwise direction and said clockwise direction so that said idler roller reverses said movement of said belt away from said normal operating position and returns said belt to said normal operating position.

31. For a conveyor having a conveyor frame, an idler roller having a roller frame pivotable on said conveyor frame, and a belt passing over said idler roller and having a normal operating position, an idler roller actuating device disposed adjacent one side of said belt and having:

a. a pivot member pivotable on said conveyor frame,

b. one member of a first tension member having a first tension member free end and a sensing arm having a sensing arm free end affixed to said pivot member,

c. a mounting member affixed to said one member,

d. the other member of said first tension member and said sensing arm mounted on said mounting member,

e. a sensing member mounted on said sensing arm free end adjacent said one side of said belt,

f. a second tension member affixed to said roller frame and having a second tension member free end pivotably connected to said first tension member free end,

g. said sensing member being engageable with said one side of said belt when said belt moves away from said normal operating position and toward said one side of said belt to rotate said sensing member and said sensing mounting member in one direction of a counterclockwise direction and a clockwise direction, and

h. said first tension member and said second tension member being operable by said rotation of said sensing member and said sensing mounting member to rotate said roller frame and said idler roller in the other direction of said counterclockwise direction and said clockwise direction so that said idler roller reverses said movement of said belt away from said normal operating position and returns said belt to said normal operating position.

32. The idler roller actuating device recited in claim 31 wherein said one member is said first tension member.

33. The idler roller actuating device recited in claim 31 wherein said one member is said sensing arm.

34. The idler roller actuating device recited in claim 11 wherein said positionable first tension member is a chain.

35. The idler roller actuating device recited in claim 12 wherein said positionable second tension member is a chain.