GB2205742A

GB2205742A - Carpet stretchers

Info

Publication number: GB2205742A
Application number: GB08804519A
Authority: GB
Inventors: Ilan Zadik Samson
Original assignee: Roberts Consolidated Industries; Roberts Consolidated Industries Inc
Current assignee: Roberts Consolidated Industries; Roberts Consolidated Industries Inc
Priority date: 1987-02-27
Filing date: 1988-02-26
Publication date: 1988-12-21
Anticipated expiration: 2008-02-26
Also published as: GB8804519D0; GB2205742B; GB8704645D0

Abstract

A carpet stretcher (1) has a head (3) which can grip the surface of a carpet connected to and able to slide relative to a body (6), a lever (10) to move the body and head apart and a releasable lock acting on the head to fix the distance between the head and the body. Further extension of the head from its locked position is possible, without having to release the tension on the stretched carpet.

Description

CARPET STRETCHERS This invention relates to carpet laying equipment and in particular relates to improvements in carpet stretchers.

Carpet stretchers are important tools in the art of carpet installation. Such tools commonly comprise a tail block which bears against a wall, an extension pole or tube connected to the tail block, and a head, having spikes to grip the carpet, slidably mounted on the extension pole. A lever is provided so that the head can be moved, by manual force, relative to the extension pole in order to exert tension on the carpet.

With the simplest carpet stretchers of the type described above, it is only possible to lock the head relative to the extension pole when the lever has been folded against the extension pole. This means that the head of the carpet stretcher must be correctly positioned on the carpet, (often with considerable difficulty) so that the correct tension is applied when the head is fully extended and locked. Numerous attempts to provide a carpet stretcher with a locking variable extension of the head have thus been made.

A device is described in U.S. Patent No. 3,692,278, in which an assembly comprising a pawl which may be moved into and out of engagement with a ratchet, enables the lever to be locked at any of many extensions. The device represents a considerable advance over earlier carpet stretchers because it is not necessary that the lever is folded against the extension pole to maintain the carpet in a stretched condition. Thus, when the carpet is stretched to the maximum extent, depression of the lever may be stopped at any of a number of positions in which the pawl and ratchet are engaged and tension on the carpet may be held until the carpet is fixed, for example by attaching it to the nails in a carpet gripper strip fixed to the floor of a room, near a suitable wall or skirting board.In the absence of such a pawl and ratchet mechanism, stretching the carpet to its maximum extent would have to be arranged to be coincident with the lever being pushed right down which, as indicated above, may involve the expenditure of a considerable amount of time and effort in the positioning of the head.

However the device disclosed in U.S. Patent No.

3,692,278 suffers from.the disadvantage that the ratchet mechanism locks the lever rather than the head, so that, when it is necessary for an operator to release the lever (for reasons discussed below) the head retracts to a certain extent and the tension on the carpet is lost.

It is commonly necessary to release the lever for two reasons. First, when one stroke of the lever is insufficient to stretch the carpet fully; it is then necessary to disengage and re-engage the lever so that a further stretching stroke can be made (an action known as 'pumping'). Secondly, when an operator finds that he can stretch the carpet no further when the lever is at a 'steep' angle in which the maximum available mechanical advantage has not been obtained.

In such a case it is desirable to reposition the carpet stretcher so that the lever assumes a position in which the angle between the lever and the horizontal plane is not so large; maximal or near maximal mechanical advantage can thus be obtained and the carpet stretched as much as possible.

In both the cormnon situations in which the lever has to be released, the device disclosed in U.S. Patent No.

3,692,278 suffers from the serious disadvantage, as indicated above, that the tension on the carpet cannot be maintained. The device also has the disadvantages that the ratchet mechanism is complex and bulky and the lever can only be locked at particular points relative to the extension pole since there are only a limited number of positions in which the ratchet can be engaged by the pawl.

The present invention provides an apparatus for use in stretching carpets, which apparatus comprises a head for gripping a carpet surface, the head being connected to and longitudinally slideable with respect to a body, R lever means for moving the head and body away from each other, and a releasable locking means for preventing the head and body from moving towards each other at any desired relative position thereof. Thus the lever means is free to be repositioned whilst the head is held fixed.

The advantage of the invention is that it provides a simple carpet stretching apparatus in which the head can be locked at any point relative to the body so that, when the lever means is repositioned to allow further extension, the head can be extended from its locked position without having to release the tension on the carpet.

In a preferred aspect of the invention the releasable locking means is attached to a first member which is attached to or integrally formed with one of the body and the head, the first member being adapted for sliding movement relative to a second member which is attached to or integrally formed with the other one of the body and the head.

A preferred locking means is described in UK Patent Application No. 8701051 and comprises: (a) an engaging means having at least two parts for engaging the inside of the first member, the engaging means defining internally a conical space; (b) a cone to fit within the conical space for sliding contact with the engaging means; the cone being operatively connected to the second member in use and moveable therewith in the direction from the base to the apex of the cone; (c) a first biasing means for urging radially the engaging means towards the cone axis against the cone; (d) a second biasing means pressing the cone axially into the conical space to force the engaging means apart against the first biasing means; and (e) means for moving the cone relative to the engaging means against the action of the second biasing means, with the proviso that the static coefficient of friction ,ul between the inner surface of the engaging means and the surface of the cone and the dynamic coefficient of friction p2 between the outer surface of the engaging means and the inside of the first member are in accordance with the equation p2 > 2,us.

Suitably the engaging means comprises at least two, preferably at least three, segments of circular cross-section, the outer surface which engage the second memberJbeing surfaced with an asbestos-free material having'a high coefficient of friction.

Advantageously, the inner surface of the engaging means is polished.

Surfacing materials known to be suitable for use in brake linings or friction wheels are excellent for the above purpose, for example friction materials sold by Ferodo under the names,terodo RC: terodo 3908F; terodo 3901F'and 'Ferodo FF: provided that 1 is suitably low.

A further valuable surfacing material is that conventionally used in engine or machine, mounting pads.

Such materials may be bonded to the outer surface of the engagement means using conventional bonding materials.

Suitably the engagement means comprises a light durable metal, suchas aluminium.

The dynamic coefficient of friction p2 as hereinabove defined is normally within the range 0.3 to 0.6, preferably within the range 0.4 to 0.6 and should not be reduced appreciably at elevated pressures.

Suitably the cone is constructed from, or surfaced with, a material having a relatively low coefficient of friction and the value of ,:l as hereinabove defined should normally be within the range 0.05 to 0.3, preferably within the range 0.05 to 0.2.

Suitably the cone is constructed from a toughened plastics material, or from toughened teflon or nylon.

Preferably the cone is made from a nylon material such as the material available from Du Pont under the Trade Mark belrin.' The first biasing means is conveniently constructed of an elastic material which is stretched around the engaging means in such a way that it does not interfere with the engagement of the inside of the first member.

Preferably the first biasing means comprises one or more rubber bands which are positioned in one or more grooves formed around the outer surface of the engagement means.

Alternatively, the first biasing means may be a circular clip of resilient material or an annular coil spring of metal or plastics.

In one preferred embodiment of the locking means, the second biasing means is a cable, and the means for moving the cone relative to the engaging means is a compression spring.

In a preferred embodiment of the apparatus of the invention, the second biasing means is a compression spring and the means for moving the cone relative to the engaging means is a cable or rod, or a combination of a cable and a rod, and which may be operated by a further small lever attached to a handle of the lever means.

In use, the releasable locking means exerts its locking action by virtue of the frictional force that is produced when the external surface of the engaging means is in contact with the inside of the first member.

Whenever the second member is moved so as to move the cone in the direction from the base to the apex of the cone, then the outer surface of the cone slides against the inner surface of the engaging means causing the outer surface of the engaging means to be pushed radially outwards. The frictional force resisting movement of the locking means within the second member is thereby increased.

It may be calculated that, for effective locking, (i.e.

for the frictional force between the engaging means and the first member to exceed the force with which the cone is being pushed into the engaging means) there are constraints on the relative values of 1, 2 and #, where a is half the conical angle. The constraints just referred to are related as follows: tan α < 2- 1 (1) 1+ 1 2 This can be approximated to: tan a < It may also be calculated that for effective unlocking without jamming i.e. due to the first biasing means, angle a and the static coefficient of friction ,: must satisfy the equation: tan a > l (2) In practice, values for a normally fall within the range 10-17 .

From formulae (1) and (2), it can be shown that

This can be approximated to p2 > 2p1 It will be apparent from the foregoing description that a locking means comprising one cone will lock the first and second members together against a compression force acting axially towards the top of the cone, but will not prevent the two members being separated if an external force acts in the opposite direction.

It is in such a form that the locking means is preferably employed in apparatus according to the present invention.

In another embodiment of apparatus of the invention, the locking means comprises two cones in symmetrical arrangement as described in U.K. patent application No. 8701051 which is incorporated herein by reference.

The lever means suitably comprises a handle connected to one of the head and body and a ratchet mounted either: (a) on the other one of the head and body with the ratchet and handle being connectable by a link member pivoted to the handle; or (b) on the handle, with the ratchet and the other of the head and body being connectable by a link member pivoted to the other of the head and body.

In a preferred embodiment of apparatus according to the invention the lever means comprises a handle connected to one of the head and body and a ratchet mounted on the other one of the head and body, the ratchet and handle being connectable by a link member.

Normally the handle is pivotally connected to the head and the ratchet is mounted on the body.

Preferably a mechanism is provided whereby the link member may be disengaged from the ratchet, when desired.

Such a mechanism suitably comprises a rod which passes through a bore formed in the handle, the rod being attached at one end to a lever device, which may be manually operated, and attached at the other end to a biasing means, preferably a tension spring which is attached to the link member. The rod is slidable within the bore and can be moved by actuating the lever device so that the link member is caused to move from, a first position, in which the link member is located within one of the spaces formed by the teeth in the ratchet, to a second position, in which the link member is disengaged from the ratchet. Advantageously, this lever device is the same as that further small lever which serves to actuate the cable or other means for releasing the locking means.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view of apparatus in accordance with the invention in use; Figure 2A is a cross-sectional view of one locking means that may be contained within such apparatus; Figure 2B is a cross sectional view of another locking means that may be contained within such apparatus; and Figure 3 shows the apparatus in side-elevation.

Referring first to Figures 1 and 3, carpet stretching apparatus 1 has a head 2 having a plurality of inclined spikes 3 the length of which protruding from the head 3 may be adjusted by a knob 4. The head 3 is attached to a body comprising in part a male tube such as a piston 5 upon which is slidably mounted a conventional steel female carpet stretcher tube 6. The female tube 6 has a number of apertures 7. By spring biased buttons (not shown), the apertures 7, allow the female tube 6 to be connected to an assembly of further carpet stretcher tubes in conventional manner. To the last tube in such an assembly in use, a tail block 8 is attached, which in use, is caused to bear against a distant abutment, usually a wall.

To the head 3 is pivotally attached, by means of a pin 9, a lever comprising a handle 10 having at one end a hand grip 11 and a further small lever 12 attached to a second biasing means comprising a cable 13 by which the releasable locking means shown in Figure 2A or Figure 2B may be actuated. A link member comprising two parallel steel strips 14, each of which is pivotally attached at one end by a pin 15 to the handle 10, connects the handle 10 to a steel ratchet 16. The ratchet 16 has teeth 17 which engage a pin 18 connecting each of the other ends of the strips 14 and is mounted on a bracket 19 attached by bolts 20 to the female tube 6. Referring now to Figures 2A and 2B, a releasable locking means 21 is attached to the end of the male tube 5 and has an aluminium engaging means 22 constructed from three segments of a circle 22A, 22B, and 22C (22C is not shown).

The segments of the engaging means 22 are pressed against a 'Delrin' cone 23 by a first biasing means comprising a metal band located in a groove 24. Each segment 22A, 22B, 22C is surfaced with a strip of machine mounting pad 25 which grips the inside of the female tube 6 when the locking means is locked (as shown in Figure 2A).

In the embodiment of the locking means 21 shown in Figure 2A, the cone 23 is fixed at its base by screws 26 to the male tube 5. A circular rod 27 attached by a pin 28 to a second biasing means comprising a cable 13 is slidably mounted through the axis of the cone Abutting the rod 27 at one end is a compression spring 29 which urges the rod 27 towards the apex of the cone 23. At the other end of the rod 27 is attached a washer 30 which abuts the engaging means 22. In the locked position shown in Figure 2A, the cable 13 has been tautened against the bias of the spring 29. To unlock the locking means, the tension on the cable 13 must be released.

In the embodiment of the locking means shown in Figure 2B, the cone 23 is fixed (by gluing or friction), or integrally formed with, a mushroom shaped member 31 having a central bore through which the cable 13 passes, thereafter separating into three strands 13A, 13B and 13C (13C not shown). A washer 30, abutting the engaging means 22, is slidably mounted on the stem 32 of the member 31 and is connected on each side of the member 31 to one of the strands 13A, 13B, 13C of the cable 13. Surrounding the stem 32 of the member 31, and bearing against the washer 30 at one end and against the head 33 of the member 31 at the other, is a circular compression spring 29 which biases the washer 30 against the engaging means 22 when the locking means 21 is in the locked position.To unlock the locking means 21, the cable 13 must be tautened, as shown in Figure 2B, by actuating the lever 12 so that the washer 30 is caused to move against the bias of the spring 29 and the cone 23 no longer presses the engaging means 22 against the inside of the female tube 6.

Referring generally to the Figures, the carpet stretcher 1 may in practice be used to stretch a carpet by a 'pumping' action of the handle 10 in which the pin 18 is caused to advance progressively along settings in the ratchet 16 formed by the teeth 17, thereby extending the head 3, and stretching the carpet incrementally. The locking means 21 is maintained in the 'locked' position throughout the stretching operation so that the compressional forcer that is experienced by the male tube 5 and female tube 6, each time the pin 18 is disengaged from the ratchet 16 is resisted, although incremental extension of the head 3 is permitted.

Claims

1. Apparatus for use in stretching carpets, which apparatus comprises a head for gripping a carpet surface, the head being connected to and longitudinally slidable with respect to a body, a lever means for moving the head and body away from each other, and a releasable locking means for preventing the head and body from moving towards each other at any desired relative position thereof.

2. Apparatus as claimed in Claim 1 in which the locking means is attached to a first member which is attached tutor integrally formed with,one of the body and the head, the first member being adapted for sliding movement relative to a second member which is attached tools integrally formed with, the other one of the body and the head.

3. Apparatus as claimed in Claim 2 in which the locking means comprises: (a) an engaging means having at'least two parts for engaging the inside of the first member, the engaging means defining internally a conical space; (b) a cone to fit within the conical space for sliding contact with the engaging means, the cone being operatively connected to the second member in use and moveable therewith in the direction from the base to the apex of the cone; (c) a first biasing means for urging radially the engaging means towards the cone axis, against the cone; (d) a second biasing means pressing the cone axially into the conical space,to force the engaging means apart against the first biasing means; and (e) means for moving the cone relative to the engaging means against the action of the second biasing means, with the proviso that the static coefficient of friction p1 between the inner surface of the engaging means and the surface of the cone. and the dynamic coefficient of friction p2 between the outer surface of the engaging means and the inside of the first member, are in accordance with the equation u2 > 2pup.

4. Apparatus as claimed in Claim 3 in which the first member is attached to or integrally formed with the body.

5. Apparatus as claimed in Claim 3 or Claim 4 in which the engaging means is of circular cross-section.

6. Apparatus as claimed in any one of Claims 3 to 5 in which the engaging means has at least three parts.

7. Apparatus as claimed in any one of Claims 3 to 6 in which the cone has a conical angle 2a where a lies in the range of from 100 to 170 (both limits included).

8. Apparatus as claimed in any one of Claims 3 to 7 in which the first biasing means comprises an elastic band, a circular clip of resilient material, or a coil spring of metal or plastics.

9. Apparatus as claimed in any one of Claims 3 to 8 in which the engaging means is surfaced with a material suitable for use in brake linings.

10. Apparatus as claimed in any one of Claims 3 to 9 in which the engaging means is surfaced with material conventionally used as engine mounting pads.

11. Apparatus as claimed in any one of Claims 3 to 10 in which the engaging means comprises aluminium.

12. Apparatus as claimed in any one of Claims 3. to 11 in which the cone comprises toughened nylon.

13. Apparatus as claimed in Claim 12 in which the cone comprises Delrin.

14. Apparatus as claimed in any one of Claims 3 to 13 in which tan a < p2 where a is half the conical angle of the cone.

15. Apparatus as claimed in any one of Claims 3 to 14 in which tan a < 2 ~ 1 - 1 + 1n2 where a is half the conical angle of the cone.

16. Apparatus as claimed in any one of Claims 3 to 15 in which

17. Apparatus as claimed in any one of Claims 3 to 16 in which > 2p1

18. Apparatus as claimed in any one of the preceding claims in which the lever means comprises a handle connected to one of the head and body and a ratchet mounted either: (a) on the other one of the head and body with the ratchet and handle being connectable by a link member pivoted to the handle; or (b) on the handle, with the ratchet and the other of the head and body being connectable by a link member pivoted to the other of the head and body.

19. Apparatus as claimed in Claim 18 in which the handle is connected to the head and the ratchet is mounted on the body.

20. Apparatus as claimed in Claim 18 or Claim 19 in which the link member can be disengaged from the ratchet by actuating a manually operated mechanism.

21. Apparatus as claimed in any one of Claims 3 to 20 in which the locking means comprises two said cones.

22. Apparatus as claimed in any one of Claims 3 to 21 in which the second biasing means comprises a spring and the means for moving the cone relative to the engaging means comprises a cable.

23. Apparatus substantially as herein described with reference to the accompanying drawings.