Clamping Systems
This invention relates to clamps, and in particular to clamps for clamping work pieces where the work piece may be expected to shrink or expand independently of work being performed on the work piece.
The most common material that is worked upon and that may be expected to shrink or expand to a degree significantly enough to affect the clamping of the work piece is wood. Other materials may, however exhibit the same properties as wood. Hereinafter, reference to wood in this document should be understood to refer to any material which may be expected to shrink or expand to a degree significantly enough to affect the clamping of the work piece. A work piece is to be understood to refer to a piece of material which is to be worked upon. Such work may include, but not be limited to sculpture or carving. Such a work piece may be, but is not limited to, a log or a bulk of timber.
At present the clamping of work pieces of wood in a position suitable to be worked upon is generally achieved using one or more of three known methods:
i) A clamp incorporating a pair of jaws which may be forced together by the rotation of a threaded bar is used to grip opposing sides of a work piece, normally at a position toward the vertically lowermost portion of the work piece. The clamp fixed to a base so as to hold the work piece in position;
ii) The work piece may be clamped between an upper jaw and a base plate when the upper jaw bears down on the work piece forcing the work piece against the base; and/or
iii) The work piece may be affixed to a base by known fixing means, such as wood screws or bolts. The size of the work piece determines the size and quantity of the fixing means needed.
All three methods have disadvantages, some of which may give rise to safety hazards. Methods i) and ii) are, in particular, hazardous when the work piece being clamped is dimensionally unstable. This is because if the work piece shrinks, wood for example shrinks when it dries, then the grip or pressure exerted by the clamps on the work piece lessens, possibly to nothing. If a worker does not rectify the lessening of the grip, that lessening may cause the workpiece to move whist being worked upon potentially damaging or harming the worker and/or the work piece. If the work piece expands then the result may be excessive compression of the work piece and/or excessive tension in the clamp mechanism which can lead to damage to the workpiece and/or the clamp mechanism.
Method iii) generally results in the work piece including within it screws or other fixing means where a worker cannot see them whilst he is working on the work piece. This has the result that a worker may strike the screw or other fixing means embedded in the work piece with a tool by accident. This may result in damage to the tool and/or the worker. This is particularly likely if a power tool is being used.
According to the present invention there is provided a clamp suitable for gripping a work piece comprising at least two jaws and a jaw support means, in which each jaw has a grip face and at least one of the jaws is provided with an actuation means adapted to move the jaw relative to the otherjaw or jaws and in which the actuation means is comprised of at least one elastically extensible tension element which when releasing tension stored therein impels the movable jaw with which it is associated in a direction that decreases the distance between the grip face of that movable jaw and the grip face of at least one of the other jaws.
The present invention is particularly advantageous over known clamps because when in use, the tension element of the actuation means is placed under tension and, in an attempt to return to a non-tensioned or relaxed state, the tension element will cause the jaw with which it is associated to move toward the otherjaw or jaws if that jaw is not prevented from doing so. The movable jaw will continue to be impelled toward the other jaws until all of the tension / stored energy in the tension element is released, or until the jaw is prevented from further movement.
If the work piece is the object blocking further movement of the movable jaw, that jaw will exert pressure on the work piece. That pressure will push the work piece towards the other jaw or jaws, and, once the work piece is pushed against the otherjaw or jaws result in the jaws gripping the workpiece. The remaining tension in the tension element, or any further tension that is introduced into the tension element is stored in the element the elastic deformation of the material of the tension element, in particular in the stretching of the tension element.
The stored tension or stored energy in the tension element has the effect that if the work piece gripped by the jaws becomes dimensionally smaller, or shrinks, the attempt by the tension element to release that energy will impel the movable jaw towards the other jaws so maintaining the grip on the work piece. Conversely, if the work piece gripped by the jaws becomes dimensionally larger, or expands, the work piece will force the or each movable jaw away from the other jaws. The tension element in the or each actuation means will resist the movement of the or each jaw, but will, when the force exerted by the work piece becomes sufficient, allow such movement by elastically deforming, as a result of an increase of the tension in the tension element.
It will be appreciated that the greater the elasticity, (or deformation per unit of applied tension), of the material of which the tension element is made, the greater the distance the movable jaw will move per unit increase or decrease in tension in the tension element. This has the effect that for a tension element made from a relatively inelastic material such as steel wire, release of a stored tension x in the tension element will cause the jaw associated with the tension element to move a particular distance whereas for a tension element made of a more elastic material, such as a nylon rope, release of a stored tension x will cause the jaw associated with the tension element to move a relatively larger distance.
It is a particularly preferred feature of the present invention that the material or materials of which the tension element is comprised may be selected so as either to determine the distance the jaw associated with the tension element will move when releasing a predetermined tension in the tension element, or to match the magnitude of the expected shrinkage or
expansion of the work piece.
In a particularly preferred embodiment of the present invention, the tension element is of a longitudinally extending shape. Most preferably the tension element is a length of a flexible material such as rope, cord, or a tape. In such an embodiment the actuation means may be so constructed that the tension element is anchored to a movable jaw at a first end, and the second end is anchored to or passes through a tensioning means wherein the tensioning means, when operated, pulls the tension element in a direction that causes the movable jaw to move toward the otherjaw or jaws. When the movable jaw is prevented from moving further toward the jaw or jaws, further operation of the tensioning means causes tension in the tension element.
In a particularly preferred embodiment of the present invention the tension element is deployed in the actuation means in a serpentine configuration. Most advantageously in a configuration in which the tension element passes around one or more pullies or bars so that the orientation of the principle axis of the tension element is not consistent along the length of the tension element. This is advantageous because it allows direction of the force caused by the tension to be different at the jaw and at the tensioning means. This has the effect that the actuation means may be of a substantially longitudinal configuration with the tensioning means located in such a position that the movable jaw moves away from the tensioning means when that jaw moves toward the otherjaw or jaws.
It is most preferred that the tensioning means is a rachet tensioner, or at least includes a rack and pawl or a rachet mechanism. Other known methods of tensioning or pulling ropes, cords or tapes may be employed as the tensioning means if so desired.
It is most preferred that the jaw support means is rigid and supports all of the jaws in a substantially single plane. In a particularly preferred embodiment, the jaw support means is substantially "y" shaped when viewed from a direction perpendicular to its principle plane. In such an embodiment, each arm of the Y supports a jaw. In an alternative embodiment, the jaw support means may be a substantially planer plate.
In a preferred embodiment the present invention the or each movable jaw is associated with an elongate slot in the jaw support means. Each movable jaw is loosely retained in its associated elongate slot, and the actuation means associated with the jaw may cause the jaw to move along the slot. Most preferably, the actuation means is fixed to the jaw support means or to a structural member which is itself, fixed to the jaw support means.
In a embodiment of the present invention, at least one of the jaws is a fixed jaw which is releaseably engagable with the jaw support means and, by virtue of it's engagement with the jaw support means, fixed in a position relative to the jaw support means. The fixing prevents movement of the jaw along the plane occupied by the jaws of the clamp- in the present invention. In a preferred embodiment, the engagement means does not prevent the or each fixed jaw being moved out of the plane occupied by the jaws in a direction substantially parallel to that plane.
hi a preferred embodiment of this embodiment, the jaw support means is provided with a plurality of positions at which or with which the or each fixed jaw may be engaged. This has the particular advantage that the positioning of the fixed jaw or jaws on the jaw support means can be optimised for the shape of the workpiece to be clamped.
The means for engaging the or each fixed jaw with the jaw support means may be studs and index holes located on the fixed jaw and the jaw support means or vice versa. The index hole may be round, or of a shape suitable for allowing the insertion of the stud at a particular position in the index hole and preventing withdrawal of the stud from the index hole at other positions in the index hole. In such configurations, it may be the case that the index hole is narrower in one or more dimensions at some parts of the mouth of the index hole than it is further away from the surface which defines the mouth of the index hole. In such embodiments, the stud may be appropriately configured so as to enable a portion of the stud adjacent to the body from which the stud projects to pass through the dimensionally smaller area of the index hole. The stud is most preferably integral with the jaw and the index holes defined by the jaw support means.
In use, a work piece is placed on the jaw support means and the or each fixed jaw located on the jaw support means so as to engage or nearly engage with a portion of the work piece. The or each movable jaw is/are then forced to move towards the work piece by it's or their associated actuation means which is being actuated by operation of the tensioning means by a worker. When the or each movable jaw engages with the work piece and is prevented from further movement, the worker continues to operate the tensioning means which introduces tension into the tension element. That tension is stored by way of elongation/elastic deformation of the tension element. The work piece can then be worked upon by a worker.
If the work piece changes dimension whilst the worker is working on it? then, if the workpiece is getting smaller, then the tension stored in the or each tension element will cause the or each moveable jaw to move towards the work piece exerting a substantially continuous or only slowly decreasing pressure. If the workpiece expands, the moveable jaw or jaws will be pushed backwards and the tension in or each the tension element will increase.
Once the worker has finished working on the workpiece, the tension in the tensioning element may be released by disengaging or reversing the operation of the tensioning means. The moveable jaw or jaws may then be pulled away from the work piece so allowing the work piece to be removed.
The present invention will be further described and explained by way of example with reference to the accompanying drawing which
Figure 1 shows a view of an embodiment of a clamp according to the present invention; and
Figure 2 shows a schematic sectional view of a portion of the clamp of Figure 1.
With reference to Figure 1, a clamp (2) is comprised of a jaw support (4) supported on legs (6). Jaw support (4) supports three jaws (8,10,12).
Jaw support (2) is of a substantial Y shape having three arms (14, 16, 18) extending from a
central junction. Two of the anus (14, 16) are substantially the same as each other and include, in their uppermost, (when the clamp for the present invention is in use), surface a plurality of index holes (20). Rigidly fixed to the free end of each of the arms (14, 16) is the leg (6) associated with that arm.
Arm (18) is provided, on it's uppermost (when the clamp in the present invention is in use) surface, with a slot (22) extending longitudinally along the arm (18). The Slot (22) is, for the majority of it's length, parallel sided. At the end of slot (22) proximal to the free end of arm (18) the slot mouths into an aperture (24). A leg (6) is rigidly afixed to the free end of the arm (18).
Jaw (12) supported on the arm (18) supported on the arm (18) is a moveable jaw and is so configured and dimensioned that it may slide along the slot (22). The jaw (12) includes a grip face (26) an upper flange (28) and a lower flange (30). Upper and lower flanges (28, 30) are so dimensioned and configured that they prevent the jaw (12) moving in a direction substantially perpendicular to the plane occupied by the arms (14, 16, 18). The lower flange (30) is also so dimensioned and configured that it may pass through aperture (24) at the end of the slot (18). This allows either the replacement of the jaw or servicing of the jaw should this prove necessary.
With reference to Figure 2, the moveable jaw (12) may be caused to move along the slot (12) in a right to left direction as shown in the figure, that is toward the grip faces of jaws (8 & 10) by being pulled by tape (32). Tape (32) has a first end (34) anchored onto the lower flange (30) of the jaw (12). The tape then passes around a first post (36) and then around a second post (38) so that the tape is direted to a tensioning means (40). The tensioning means (40) is most preferably a rachet tensioner of a known construction. The first and second posts (36, 38) may either be fixed posts with at least one end rigidly fixed to the arm (18). Alternatively, the first and second posts (36, 38) may be comprised of an axle and bearing or pulley so that the tape (32) may pass smoothly around the posts. Post (36) is located at a position at least as far from the free end of arm (18) as the end of slot (22) distal from that free end.
In use, a log (42) shown in dashed lines on Figure 1 is placed on the jaw support means (4) and the fixed jaws (8, 10) engaged with appropriate index holes (20) via studs (not shown) so as to be adjacent to or engaged with log (42). Jaw (12) has, in the meantime, been pulled back toward the free end of the arm (18) so as to be out of the way of log (42). Once the fixed jaws (8, 10) have been suitably located tensioning means (40) is used to pull the tape (32) causing jaw (12) to travel along the slot (22) towards the log (42). Once grip face (26) of the jaw (12) engages with the log (42) the worker continues to operate the tensioning means (40) so bringing grip face (26) into pressured contact with the log (42) and, subsequently, introduces tension into the tape (32) causing the tape to stretch. If the log (42) expands then the jaw (12) is pushed in a left to right direction (as shown in Figure 2) causing an increase in the tension in tape (32). If the log (42) shrinks, the tape (32) seeks to release tension by becoming shorter so moving jaw (12) in a right to left direction (as shown in Figure 2) thus maintaining the grip of grip face (26) on log (42).
It will be appreciated that although the embodiment of the present invention illustrated in Figures 1 and 2 includes only one mobile jaw and three jaws in total, the principles of the present invention can be applied to a clamp including more than one mobile jaw and/or two or more than three jaws in total. Likewise, the tape (32) can be replaced by an appropriate alternative tension element such as a rope or a cord. Equally the tensioning means (40) could be mounted on the arm (18) should that be so desired.