Information
-
Patent Grant
-
6705179
-
Patent Number
6,705,179
-
Date Filed
Friday, September 29, 200024 years ago
-
Date Issued
Tuesday, March 16, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Quarles & Brady
- Walbrun; William R.
-
CPC
-
US Classifications
Field of Search
US
- 074 505
- 074 545
- 074 606 R
- 074 506
- 024 7121
- 024 7125
- 024 7135
- 024 134 R
- 024 136 R
- 024 134 KA
- 254 335
- 254 337
- 254 338
-
International Classifications
-
Abstract
A rope tensioner sets the tension of a rope operated switch assembly actuable to switch between first and second conditions on a change in tension of the rope. The tensioner comprises a body, a rotatable member which engages the rope, a shaft for rotating the member relative to the body to adjust tension in the rope by winding the rope around the member, and a lock to lock the member in position relative to the body. The rope opperated switch assembly is much simpler to install than previous assemblies, as the tensioner may be simply threaded or otherwise installed onto the rope without the rope having to be cut.
Description
TECHNICAL FIELD
The present invention relates to a rope tensioner which may be used to tension a rope operated switch assembly. Such an assembly may be used, particularly but not exclusively for controlling the power supply to kinetic machinery.
BACKGROUND ART
Rope operated switch assemblies are generally fitted in proximity to a machine or around any area which requires protection, and comprise two safety switches and a rope extending between the switches such that the electrical power supply may be turned off when the rope is pulled or slackened (e.g. if the rope is cut). In some applications, only one switch is provided, the end of the rope being connected to the single switch and the other end being connected to for example a spring secured to a fixed point. The rope is generally a plastics-coated metal wire or cable, and extends around the machine so that an operator can easily reach it from any position adjacent the machine. The term “rope” used hereinafter is intended to mean any elongate flexible element that is suitable for using in a rope operated switch assembly, for example, metal cable, cord formed of twisted elements or fibres such as wire, polymeric material, etc., which may optionally be coated with a plastics material.
The rope must be installed at the correct tension so that the machinery can be operated but so that a relatively small change in the tension of the rope will actuate the switch assembly. This is important because an injured operator may not be able to pull the rope with much force.
The installation of the rope at the correct tension is difficult to achieve. The rope must first be installed between the two switches, and is then pulled into an approximation of the correct tension. A turnbuckle is installed in the centre of the rope by cutting the rope and fixing the turnbuckle between the rope sections using thimbles and cable clamps. Once installed, the tension in the rope is set by adjusting eye bolts on the turnbuckle until the rope switches are pulled into a “run” position, that is, with safety contacts in the switches made. The turnbuckle then allows small alterations to be made to the tension of the rope to allow for expansion or contraction of the rope due to, for example, temperature differences.
Placement of the turnbuckle in the rope is a time-consuming and often difficult process, and can take up a large proportion of the total time taken to install the rope switch assembly. The setting of the correct tension in the rope is particularly difficult, as the switches must be continually checked to ensure that the switch mechanisms are in the correct position in order that the rope is not set at an incorrect tension. As the turnbuckle ideally is placed towards the centre of the rope to allow for even tensioning, the turnbuckle may be some distance from the switches.
In addition, the turnbuckle only allows small differences in tension in the rope to be corrected for. If the tension alters by more than can be dealt with using the turnbuckle, the slack or expansion must be dealt with by movement of the thimbles and cable clamps along the rope segments. A large alteration in tension can occur, for example, due to large temperature fluctuations in different seasons, especially on long runs of rope.
DISCLOSURE OF INVENTION
It is an object of the present invention to obviate or mitigate such disadvantages with prior art systems.
According to a first aspect of the present invention there is provided a rope operated switch assembly comprising a rope extending to at least one switch, the switch being actuable to switch between first and second conditions on a change in tension of the rope, and a tensioner for setting the tension of the rope, wherein the tensioner comprises a body, a rotatable member which engages the rope, means for rotating the member relative to the body to adjust tension in the rope by winding the rope around the member, and locking means to lock the member in position relative to the body.
The tensioner may be simply threaded or otherwise installed onto the rope during installation of the rope operated switch assembly, without the need to cut the rope. The installation is thus much simpler than with prior art switch assemblies.
The locking means preferably comprises a ratchet and pawl. Preferably, means displaceable relative to the body are provided to move the pawl out of engagement with the ratchet, thereby unlocking the shaft to release the tension in the rope. The displaceable means may comprise a screw that may be screwed into the body.
A plate is preferably provided to separate the tensioner into two compartments, the rope extending into one compartment, and the locking means being provided in the other compartment. This means that the rope does not become entangled in the locking means whilst the tensioner is being installed along the rope.
The tensioner is preferably provided adjacent the switch, meaning that the installation may be effected quickly as the operator can easily check the state of the adjacent switch as the tension in the rope is altered.
According to a second aspect of the present invention there is provided a method of installing a rope operated switch assembly comprising connecting the rope to at least one switch which is actuable to switch between first and second conditions on a change in tension of the rope, the rope being initially installed such that an approximation of the correct tension is achieved in the rope, and increasing the tension in the rope by means of a tensioner, wherein the tensioner comprises a body and a rotatable member which engages the rope, the tension in the rope being increased by rotating the rotatable member relative to the body such that the rope is wound around the member, and locking the rotatable member in position relative to the body after the rope has been tensioned.
The tension of the rope is preferably monitored as the tension is increased by viewing a tension indicator provided on the at least one switch. The tensioner is preferably placed close to an end of the rope, adjacent to the at least one switch, for ease of viewing of the tension indicator provided on the switch.
Unlocking means are preferably provided in the tensioner so that the tension of the rope may be released.
According to a third aspect of the present invention, there is provided a rope tensioner comprising a body defining a passage through which a rope can be inserted to project from each end of the passage, a member rotatable relative to the body and formed to engage a rope extending through the passage such that rotation of the member causes the rope to be wound around the member, and means for locking the member in position relative to the body to resist unwinding of the rope from the member.
The means for rotating the rotatable member around which the rope is wound may be a drive member mechanically coupled by a gear to the rotatable member. The drive member may be a worm gear meshed with a gear supported by the rotatable member. The locking means may be provided by providing a gear system with a mechanical advantage such that unwinding of the rope from the rotatable member is prevented unless the drive member is rotated to drive the rotatable member in a direction to unwind the rope.
The rotatable member is preferably a shaft defining an aperture aligned with openings in the tensioner body.
The locking means preferably comprises a ratchet and pawl assembly.
Preferably the tensioner comprises means for releasing the locking means.
BRIEF DESCRIPTION OF DRAWINGS
An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:
FIG. 1
is a plan view of a rope operated switch assembly according to the present invention;
FIG. 2
is an exploded perspective view of a tensioner for use in the rope operated witch assembly of
FIG. 1
;
FIG. 3
is a perspective view of the base of the tensioner of
FIG. 2
;
FIG. 4
is a perspective view of the base of the tensioner of
FIG. 3
, with a cover plate; and
FIG. 5
shows perspective views of the tensioner from different viewpoints.
FIG. 6
is a perspective exploded view of a second embodiment of the present invention;
FIG. 7
is a view from above of a base component of the embodiment of
FIG. 6
showing a spindle engaged by a worm drive; and
FIGS. 8 and 9
show the embodiment of
FIG. 6
after removal of a cover and illustrating successive stages in the winding of a rope onto the spindle.
BEST MODES FOR CARRYING OUT THE INVENTION
Referring to
FIG. 1
of the accompanying drawings, there is illustrated a rope operated switch assembly comprising a first switch
1
, a second switch
2
, a rope
3
extending between the switches and a tensioner
4
installed along the rope.
The switches
1
and
2
are of any suitable design, and may be as described in WO-A-97/20334, for example. The switches are such that two tension thresholds are established. The first, lower threshold is such that unless the tension of the rope exceeds the first threshold the switch cuts off the supply of power required to enable the machinery to be operated. The second, higher threshold is such that unless the tension on the rope is less than the second threshold, the switch again acts to cut off the supply of power to the machinery. The switches
1
,
2
each comprise a tension indicator
5
, an emergency stop button
6
, and a reset knob
7
. Each switch also comprises a tubular body extension
8
which receives a spring-loaded shaft
50
(shown in phantom) attached to a rotatable D-ring connector
9
. The switches are mounted such that the distance between the D-rings
9
is generally less than 75 meters.
The rope
3
is PVC coated steel cable, although any suitable rope may be used. The rope is attached between the switches
1
,
2
by passing the rope around suitable thimbles looped through the rings
9
and clamping the rope ends in clamps
10
, in a known manner. The rope is supported along its length by means of a plurality of eye bolts
11
placed at distances of 2 to 3 meters apart along the machinery.
The tensioner
4
is further illustrated in
FIGS. 2
to
5
. The tensioner comprises a base
12
and top
13
. The base
12
comprises four apertures
14
to allow screws
15
to be screwed into corresponding threaded apertures (not shown) on the top
13
to hold the tensioner together. A pawl
16
is mounted on a spindle
17
, and is acted on by a spring
18
. A threaded aperture
19
allows a screw
20
to be screwed into engagement with the pawl
16
, to push it against the biasing force of spring
18
. A circular wall
21
is provided in the base to form a recess, the wall
21
having a section
22
of reduced height over which the pawl extends.
Two further apertures
23
are provided in base
12
, one at either end thereof, to enable the tensioner to be threaded onto the rope
3
.
A rotatable spindle
24
is provided in the tensioner, having an aperture
25
therethrough, and having a ratchet-toothed wheel
26
provided at one end thereof. The aperture
25
may be aligned with apertures
23
as shown so that the rope may be pushed through one aperture
23
, the aperture
25
, and the other aperture
23
. A hexagonal recess
27
is provided in one end of the spindle
24
which extends through the top
13
, suitable to allow the spindle to be turned using an Allen key. The end of the spindle having the recess
27
is further provided with an arrow-shaped indicator to indicate when the aperture
25
is aligned with the apertures
23
. The ratchet-toothed wheel
26
sits in the circular recess created by wall
21
in the base
12
.
A cover plate
28
is provided between the base
12
and top
13
, having an aperture
29
in the centre thereof such that the spindle
24
may pass through the aperture leaving the toothed wheel
26
between the cover plate and the base
12
so that the aperture
25
is positioned between the cover plate and the top
13
.
To install the rope operated switch assembly, the tensioner
4
is threaded onto the rope
3
, and the rope is installed between switches
1
and
2
. The rope
3
is pulled to an approximation of the correct tension during installation. The cover plate
28
allows the rope to be easily threaded through the tensioner
4
without becoming entangled in the toothed wheel
26
and pawl
16
.
The tension in the rope
3
is then increased by turning the spindle
24
using an Allen key. This causes the rope extending through the spindle
24
to be wound about the spindle from both sides, thereby increasing the tension on the rope. The tension is maintained on the rope due to the ratchet and pawl preventing the spindle from turning in the wrong direction. The tension of the rope
3
is monitored by means of the tension indicators
5
provided on switches
1
,
2
. The tensioner
4
may be installed on the rope near to one of the switches so that it is easy for the operator to monitor the tension of the rope.
The tension may be released if necessary by tightening the screw
20
, which pushes on the pawl
16
to release it from the ratchet-toothed wheel
26
. The rope can then be pulled to release some of it from the tensioner, and the screw
20
can be unscrewed to re-set the ratchet and pawl. The tension in the rope may then be increased again by turning spindle
24
.
If the tension in the rope alters over time, for example owing to temperature variations, friction and wearing of the rope caused by mis-aligned eye-bolts, etc, the tension may be simply re-set by either turning the spindle to tighten the rope, or by releasing the pawl to unlock the tensioner.
To operate the machinery, the tension of the rope is adjusted so that switches
1
and
2
are in the “run” position between the two tension thresholds. If the tension on the rope is then increased (i.e. by an operator pulling the rope), or decreased (i.e. if the rope is cut), the switches
1
and
2
are tripped, and the power to the machine is cut, preventing it from operating.
It should be appreciated that various modifications to the exemplary embodiment may be made. For example, the spindle may be held in position by a locking mechanism other than a ratchet and pawl.
The tensioner may be attached to only one end of the rope and connected to a switch by, for example, a hook passed through the ring
9
. In this instance, the end of the rope that is connected to the tensioner would have to be securely attached to the spindle.
Although in the illustrated embodiment the tensioner is attached to the rope before the rope is connected to the or each switch, the tensioner could be attached to the rope after it has been installed, to allow for retro-fitting of existing rope operated switch assemblies. For example, the tensioner could comprise hooked attachment means that may be used to connect the tensioner to the rope, the rope becoming engaged in a separately rotatable member in the tensioner body.
Referring now to
FIG. 6
, this illustrates an alternative embodiment of the invention. Whereas in the case of the embodiment of the invention illustrated in
FIGS. 1
to
5
the spindle
24
is rotated by inserting a suitable tool into a recess provided in one end of the spindle, in the embodiment of
FIG. 6
the rope is tensioned by rotating a spindle using a worm drive gear arrangement.
Referring in detail to
FIG. 6
, the illustrated embodiment of the invention comprises a base
30
, a top
31
, and an intermediate plate or rope confining partition
32
which is sandwiched between the base and top, the three components being secured together by screws
33
to form a body defining an open-ended passage
51
receiving the rope. A spindle
34
supports gear teeth
35
, the spindle being received within a socket
36
moulded into the base
30
and extending through an opening
37
in the plate
32
. The spindle
34
defines a hole
52
(see
FIG. 8
) through which a rope
38
to be tensioned is inserted.
A worm drive
39
aligned with an aperture
40
in the base has a flanged end
41
which is received in a socket
42
defined by the base. The worm
39
is retained between the base
30
and plate
32
and engages the gear
35
. A tool may be inserted through the opening
40
to engage in a socket
41
defined in the end of the worm
39
to enable the rotation of the worm about its axis, such rotation causing the spindle
34
to rotate about its axis as a result of the interengagement of the worm
39
and the gear
35
. Thus the rope
38
can be caused to wind around the spindle
34
.
FIG. 7
shows the base
30
, spindle
34
.and worm drive
39
before the plate
32
is mounted on the base.
FIGS. 8 and 9
show the embodiment of
FIG. 6
after removal of the top cover
31
and insertion of a rope.
FIG. 8
shows the rope wound around the spindle
34
after the spindle has been turned through slightly more than 90°, and
FIG. 9
shows the rope after further rotation of the spindle. It will be appreciated that the manner in which the rope is wound around the spindle as shown in
FIGS. 8 and 9
is the same as the manner in which a rope is wound around the spindle
24
in the embodiment of
FIGS. 1
to
5
.
In contrast to the embodiment of
FIGS. 1
to
5
, in the case of the embodiment of
FIG. 6
tension in the rope can be closely controlled as a rotation through 360° of the worm
39
causes a relatively smaller rotation of the spindle
34
. Furthermore, the mechanical advantage provided by the gearing system can be such that it is unnecessary positively to lock the worm
39
in a position to which it has been rotated. This means that the installer can increase or decrease the rope tension by simple rotation of a tool inserted into the socket
41
, enabling very fine adjustment to the rope tension. Additional locking means (not shown) may however be provided to positively lock the worm and spindle
5
in the positions to which they have been rotated.
Claims
- 1. A rope tensioner comprising a body defining a passage through which a rope can be inserted to project from each end of the body, a member rotatable relative to the body and formed to engage the rope extending through the passage such that rotation of the rotatable member causes the rope to be wound around a full periphery of the rotatable member, and a partition disposed within the body to confine the rope wound around the rotatable member.
- 2. A rope tensioner according to claim 1, further including a drive mechanically coupled to the rotatable member to rotate the rotatable member relative to the body.
- 3. A rope tensioner according to claim 2, wherein the drive member includes a first gear that meshes with a gear supported by the rotatable member.
- 4. A rope tensioner according to claim 3, wherein the first gear is a worm gear.
- 5. A rope tensioner according to claim 4, wherein the first gear and the gear supported by the rotatable member have a mechanical advantage such that unwinding of the rope from the rotatable member is prevented unless the first gear is rotated to drive the rotatable member in a direction to unwind the rope.
- 6. A rope tensioner according to claim 1, wherein the rotatable member is a spindle defining an aperture aligned with openings in the tensioner body.
- 7. A rope tensioner comprising a body defining a passage through which a rope can be inserted to project from each end of the body, a member rotatable relative to the body and formed to engage the rope extending through the passage such that rotation of the rotatable member causes the rope to be wound around the rotatable member, means for rotating the rotatable member relative to the body, the rotating means comprising a drive member mechanically coupled by a gear to the rotatable member, and a partition disposed within the body between the rope and the drive member.
- 8. A rope tensioner according to claim 7, wherein the drive member is a worm gear meshed with the gear supported by the rotatable member, the mechanical advantage of the gear system being such that unwinding of the rope from the rotatable member is prevented unless the drive member is rotated to drive the rotatable member in a direction to unwind the rope.
- 9. A rope tensioner according to claim 8, wherein the rotatable member is a spindle defining an aperture aligned with openings in the tensioner body.
- 10. A rope tensioner according to claim 7, wherein the rotatable member is a spindle defining an aperture aligned with openings in the tensioner body.
- 11. A rope tensioner comprising a body defining a passage through which a rope can be inserted to project from each end of the body, a member rotatable relative to the body and formed to engage the rope extending through the passage such that rotation of the rotatable member causes the rope to be wound around the rotatable member, and a partition disposed within the body to confine the rope wound around the rotatable member, wherein the rotatable member is a spindle defining an aperture aligned with openings in the tensioner body.
- 12. A rope tensioner comprising a body defining a passage through which a rope can be inserted to project from each end of the body, a member rotatable relative to the body and formed to engage a the rope extending through the passage such that rotation of the rotatable member causes the rope to be wound around the rotatable member, a first gear meshed with a gear supported by the rotatable member to rotate the rotatable member relative to the body, and a partition disposed within the body to confine the rope wound around the rotatable member.
- 13. A rope tensioner according to claim 12, wherein the first gear is a worm gear.
- 14. A rope tensioner according to claim 12, wherein the first gear and the gear supported by the rotatable member have a mechanical advantage such that unwinding of the rope from the rotatable member Is prevented unless the first gear is rotated to drive the rotatable member in a direction to unwind the rope.
- 15. A rope tensioner according to claim 12, wherein the rotatable member is a spindle defining an aperture aligned with openings in the tensioner body.
- 16. A rope tensioner comprising a body defining a passage through which a rope can be inserted to project from each end of the body, a member rotatable relative to the body and formed to engage the rope extending through the passage such that rotation of the rotatable member causes the rope to be wound around the rotatable member, a drive member mechanically coupled by a gear to the rotatable member to rotate the rotatable member relative to the body, and a partition disposed within the body between the rope and the drive member.
US Referenced Citations (24)
Foreign Referenced Citations (9)
Number |
Date |
Country |
555340 |
Mar 1957 |
BE |
324480 |
Nov 1957 |
CH |
004320854 |
Jan 1995 |
DE |
001136723 |
Sep 2001 |
EP |
001255262 |
Nov 2002 |
EP |
1047211 |
Jan 1966 |
GB |
57-191189 |
Nov 1982 |
JP |
2-191830 |
Jul 1990 |
JP |
WO 9720334 |
Jun 1997 |
WO |