GB2072545A

GB2072545A - Self-clamping jig

Info

Publication number: GB2072545A
Application number: GB8107863A
Authority: GB
Original assignee: Gersan Ets
Current assignee: Gersan Ets
Priority date: 1980-03-24
Filing date: 1981-03-12
Publication date: 1981-10-07
Also published as: GB2072545B

Abstract

A self-clamping holder has a locating surface formed by pads 6 for engaging a locating face 2 on the object 1, a clamping roller 52 and a reaction roller 54 on opposite sides, for holding the sides 3 of the object. The clamping roller 52 acts as a sprag-clutch element, being biased upwards into its clamping position and bearing against an inclined backing wall 47. The reaction roller 54 acts as a locating element, rotating about a fixed axis, but it is also associated with a free-wheel device formed by a clutch roller 63 resting between the reaction roller and a vertical backing wall 49, permitting the reaction roller to rotate only in the direction of insertion of the object. The object 1 can be inserted into the holder in a direction at right angles to the locating pads and is clamped in position by the automatic action of the clamping roller. To release the object, a releasing plunger pushes down the clamping roller. <IMAGE>

Description

SPECIFICATION Self-clamping jig Background of the Invention The holder of the present invention was developed in order to locate and clamp the gemstone holder described in British Published Patent Specification 2 052 369, but the holder of the present invention has generally applicability, particularly where a 6-point (kinematic) location is required, though the holder of the invention can also be used where kinematic location is not required and can thus be designed in such a way that kinematic location is not provided.

The Invention The present invention provides holders as set forth in Claims 1 and 25. The remaining claims set forth preferred features of the invention.

The holder of the invention can be very rapid in action. The object is inserted until it is stopped by the locating surface, which enables the object to be properly located. The insertion of the object causes automatic gripping of the object by the clamping element(s), which is biased (normally spring biased). The clamping element will be arranged to resist movement of the object away from the locating surface, i.e. such that its clamping force increases with slight movement of the object away from the locating surface. To release, the clamping element would normally be moved in a direction generally towards the locating surface. Release can be extremely simple using the releasing means, which can be a manually depressable plunger or other means which acts positively on the clamping element to move it away from its clamping position.The holder in effect is a self-clamping jig, and, in addition to clamping diamond and other gemstone holders, it has general applicability in the jig and tool industry, for instance for holding workpieces for drilling. In general, the workpiece can be rough, but it must be approximately the right size and said side faces must be roughly parallel (as seen in section normal to the locating surface) and are preferably strictly parallel-the side faces are preferably planar, but could be the opposite sides of say a cylindrical object with suitable design of the holder.

Although the reaction element could merely be represented by a planar wall, it is found that in practice, a somewhat more elaborate reaction element may be required, partly because a planar wall could enable the object to be lifted up from one edge and to rock and thus may not lead to secure clamping, and partly because a planar wall could lead to difficulty in insertion; the most satisfactory solution to both these disadvantages has now been discovered to be that of using a circular section reaction element which can rotate in the sense corresponding to the insertion of the object but cannot rotate in the other sense.

The clamping and reaction elements are preferably of circular cross-section, for instance short rollers or spheres, but they could be other shapes, for instance prisms such as rhomboidal or parallelogram prisms. The clamping elements can be positively retained (e.g. pivoted on a fixed fulcrum) or merely resting in position, e.g. as a sphere against a backing surface. In general, the clamping elements can be small, i.e. narrow compared with the width of the object and short compared with the height of the object.

The backing surfaces (against which the rear sides of the clamping elements can bear) are not essential as e.g. pivoting clamping elements such as pawls or eccentrically pivoted rollers can be used. However, if the inclined backing surfaces are used, the angle of inclination can be called the locking angle.

The preferred locking angle is 10, to 1 5,, but a wider preferred range 7.5 to 17.5 . It will be appreciated that the smaller the locking angle, the better the clamping effect, but the more movement than can occur before full clamping occurs, and vice versa. As the backing surface could be just a backing sphere or a roller against which a clamping sphere or roller bears, the inclination of the backing surface is the inclination at the point of contact with the clamping element when the object is held in position.

Preferred Embodiments The invention will be further described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a plan view of a self-clamping holder in accordance with the invention; Figure 2 is a section along the line ll-ll in Fig. 1, also showing the base of an object being clamped; Figure 3 is a view, partly in vertical section, through a second self-clamping holder in accordance with the invention; Figure 4 is a plan view of a third selfclamping holder in accordance with the invention; and Figures 5 to 10 are vertical sections along the lines indicated in the conventional manner in Fig. 4.

First Embodiment of the Invention As can be seen in Fig. 2, the base 1 of the object being clamped in the holder of Figs. 1 and 2 is in the form of a cube with a bottom, locating face 2 and sides 3.

The holder 4 has a base 5 which forms a locating surface by means of three co-planar pads 6 which are the heads of small studs 7.

The locating surface is encompassed by four walls 8, 9, 10, 11, and the wall 10 can act as the support for the holder. Each pair of opposite walls has respective clamping and reaction elements, and those of the walls 8 and 10 will be described first.

As can be seen in Fig. 2, there is a clamping element in the form of a spherical ball 12 which is contained at the top of an inclined bore and spring biased upwards by a helical compression spring 1 3 held by a screwed-in plug 14. The ball 1 2 acts as a sprag clutch element with its front, exposed side engaging the side 3 of the object and its rear side bearing against a backing surface (formed by the rear wall of the bore) which makes a small angle of inclination to the vertical and is inclined inwards so that a clamping action is provided as the object (1) is removed from the holder 4.In its uppermost position, at the top end of the bore, to which the ball 12 is biased by the spring 1 3, the bore has one part of its circumference open towards the interior but the remainder of the circumference passes around more than 180 of the ball 12, thereby preventing the ball 12 rolling out.

Above the ball 12 there is a small gravitybiased plunger 15 which can be depressed manually to move the ball 1 2 downwards and release the object, thereby acting as releasing means.

The other wall 10 has an inclined, part cylindrical bore drilled in it, terminating in a seat 1 6 on which rests a ball 1 7, which acts as a locating/reference and reaction element.

Likewise the bore forms an inclined backing surface and, in the lowermost part of the bore, its circumference passes round more than 180 of the ball 1 7, thereby preventing the ball falling out. The ball 1 7 will normally rest in its seat 16, and therefore provides a location in a predetermined position for the respective side wall 3. In each case however, the balls 1 2 and 1 7 can move generally at right angles to the locating surface, and it is this possibility of movement which provides the clamping action should a withdrawal force be applied to the object (1).

As can be seen in Fig. 1, there is a further ball 1 8 in the wall 10, the balls 1 7 and 18 being adjacent the edges of the wall 10 and the ball 1 2 being in the middle of the wall 8, as seen looking down as in Fig. 1. There is a small apertured plate 1 9 which guides the plunger 1 5 and also prevent it falling out.

The remaining two walls 11, 9 have respectively one clamping ball 20 and one reaction ball 21, these balls being near one edge of each wall 9, 11, as can be seen in Fig. 1. The clamping ball 20 and associated arrangement is like that of the clamping ball 12, and its release plunger 22 can be seen in Fig. 1, whilst the reaction ball 21 and its arrange ment is like that of the reaction ball 1 7.

Holder 4 is designed such that all the balls 12,17, 18, 20 and 21 are at the same height when the object (1) is in position.

The object (1) is inserted into the holder 4 in a direction at right angles to the locating pads 6 and is clamped in position solely by the action of the clamping balls 12, 20. In order to release the object (1), the release plungers 1 5, 22 must be depressed.

In practice, it has found that the reaction balls 17, 18, 21 make it difficult to insert the object (1) or even jam it as they themselves cannot rotate freely. This could be avoided by a free-wheel arrangement for the reaction balls 17, 18, 21, and a free-wheel arrangement as applied to rollers is described with reference to Figs. 4 to 10 below.

Second Embodiment of the Invention The holder 31 of Fig. 3 is not described in full detail, but it illustrates two possible modifications of the holder 4 of Figs 1 and 2.

The wall 32 is guided by a slideway (not shown) and is located by a screw-threaded adjustment spindle 33 so that the size of the holder 31 can be adjusted for different sized objects. However, the spindle 33 is used only for adjustment and not for clamping. The sprag-clutch clamping and reaction elements are parallelogram prisms 34, each of which may be biased into its clamping position by helical compression springs 35. As in the case of the holder 4, a clamping action is provided as the object is removed from a locating surface 36, but in this case, there is no necessity for an inclined backing surface.

Third Embodiment of the Invention The holder 41 shown in Figs. 4 to 10 has a base plate 42 which carries an adjustment ring 43 guided by an annular, bronze locating bearing 44 and fixed by two knurled screws 45. This provides for a small angular adjustment of about + 5 . The three pads 6 which form the locating surface are mounted on the base plate 42 while the mounting ring 43 mounts four walls 46, 47, 48, 49 encom passing the pads 6 and in turn carrying a frame-like cover plate 50.

The clamping and reaction elements are in the forms of rollers 51, 52, 53, 54, mounted on respective spindles 55, 56, 57, 58. Although all the rollers 51-54 could be cam bered or all cylindrical, it is preferred that only the clamping rollers 51, 52 be cambered (alternative terms are crowned or bomber and that the reaction rollers 53, 54 be cylindrical; cambered rollers give near point contact and press elasticly into the object (1), giving a higher locking force, whereas the cylindrical rollers have a longer bearing surface and give a more accurate kinematic reference face.

The clamping rollers 51, 52 are each mounted on a spindle 55, 56 (see Figs. 7 and 8) one end portion of which is pivoted by mounting in a self-aligning bearing 59 and the other end portion of which is in the form of a ball which can move generally towards the locating s r, .e, thereby canting the re spective spindle 55, 56 to move the clamping roller 51, 52. As shown in Fig. 8, the ball end of the spindle 55 rests on a small springbiassed plunger 60 which biasses the clamping roller 51 in the direction of removal of the object (1) from the locating surface. In a somwhat similar manner, the ball end of the spindle 56 engages in a cross-bore in a spring-biassed release plunger 61, thereby biassing the clamping roller 52 in the direction of removal of the object (1) from the locating surface.Adjacent the ball end of the spindle '56, the end portion of the spindle 56 crosses over the end portion of the spindle 55 so that depression of the release plunger 61 cants both spindles 55, 56 generally towards the locating surface and thereby moves both clamping rollers 51, 52 generally towards the locating surface, for releasing the object (1).

Each clamping roller 51, 52 bears against an inclined backing surface formed on the wall 46, 47 (see Figs. 7, 8 and 9), the clamping rollers 51, 52 thus acting as spragclutch elements.

The reaction roller spindles 57, 58 are carried between fixed self-alligning bearings 59 and are thereby fixed in position though freely rotatable in one sense (see Figs. 5 and 10). However, a free-wheel device is formed which permits rotation in the sense corresponding to the insertion of the object (1) into the holder 41 but prevents rotation in the opposite sense; cylindrical clutch rollers 62, 63 rest by gravity between the respective reaction roller 53, 54 and a vertical backing wall 48, 49 (see Figs. 6, 7 and 9).

It will be seen that there is a single clamp ing roller 51, 52 and a single reaction roller 54 on three sides, whereas on the fourth side there are two reaction rollers 53. The reaction rollers 53, 54, in association with the pads 6, form a six-point kinematic location for the object (1).

The object (1) can be inserted into the holder 41 in a direction at right angles to the locating surface, entry being freely permitted by the rotation of the reaction rollers 53, 54 and the rotation and slight depression of the clamping rollers 51, 52. The object (1) is then clamped in position solely by the action of the clamping rollers 51, 52 against the reaction of the reaction rollers 53, 54. The object (1) can be easily released by depressing the plunger 61.

Claims

1. A self-clamping holder for holding an object having a locating face and two opposite sides making a substantial angle with the locating face, the holder comprising: a locating surface for engaging the locating face of the object; at least one clamping element for engaging and holding a respective said side of the object, the clamping element acting as a sprag-clutch element and being biased into its clamping position; at least one reaction element for engaging the opposite said side of the object; and releasing means for moving the clamping element or the reaction element, to release the object; whereby the object can be inserted into the holder in a direction generally at right angles to said locating surface and is clamped in position by the automatic action of the clamping element or elements.

2. The holder of Claim 1, wherein the reaction element also acts as a sprag-clutch element.

3. A self-clamping holder for holding an object having a locating face and two opposite sides making a substantial angle with the locating face, the holder comprising: a locating surface for engaging the locating face of the object; a clamping element whose front, exposed side will engage a respective said side of the object, the clamping element being movable generally at right angles to the locating surface; a backing surface against which the clamping element can bear, the backing surface being inclined as seen looking along the plane of the locating surface, the inclination being small and being such that a clamping action is provided by the respective clamping element as the object is removed from the locating surface; biasing means biasing said movable clamping element in the direction of removal of the object from the locating surface;; a reaction element whose front, exposed side will engage the opposite said side of the object; and releasing means for moving the clamping element or the reaction element, to release the object; whereby the object can be inserted into the holder in a direction generally at right angles to said locating surface and is clamped in position by the automatic action of the clamping element or elements.

4. The holder of Claim 3, wherein the reaction element is movable generally at right angles to the locating surface, and there is a backing surface against which the reaction element can bear, the backing surface being inclined, as seen looking along the plane of the locating surface, the inclination being small and being such that a clamping action is provided by the reaction element as the object is removed from the locating surface.

5. The holder of any one of the preceding claims, wherein the reaction element always has the same location whenever the object is clamped.

6. The holder of Claim 5, wherein the reaction element normally rests against a seat in its position furthest from the respective side of the object, thereby being located in a predetermined position for location of the respective side of the object.

7. The holder of any one of Claims 1 to 5, wherein the reaction element has at least a circular (as seen in section at right angle to the locating surface) surface which contacts the respective side of the object, and can rotate about the centre of the circle, the reaction element being associated with a freewheel device which permits rotation of the reaction element in the sense corresponding to the insertion of the object into the holder but prevents rotation in the opposite sense.

8. The holder of Claim 7, wherein the reaction element is circular (as seen in section at right angles to the locating surface) and the free-wheel device is a clutch element of circular section (as seen in section at right angles to the locating surface), resting between the reaction element and a backing wall.

9. The holder of any one of the preceding Claims, wherein the clamping and/or reaction element is of circular shape (as seen in section at right angles to the locating surface).

10. The holder of Claim 9, wherein the clamping and/or reaction element is spherical.

11. The holder of Claim 10, wherein the clamping and/or reaction element is contained in a part-cylindrical bore.

1 2. The holder of Claim 11, wherein the bore is formed in a surface which will face the respective side of said object, the bore axis being inclined relative to the surfaces in which it is formed and, in the clamping position of the clamping element, the bore having part of its circumference which is open towards the position of the respective side of the object but the remainder of the circumference passing round more than 180 of the clamping element.

1 3. The holder of Claim 9, wherein the clamping element and/or the reaction element is a roller which has a length greater than its diameter.

14. The holder of Claim 9 or 1 3, wherein the clamping element and/or the reaction element is a cambered roller.

1 5. The holder of Claim 14, wherein the or each clamping element is a cambered roller and the or each reaction element is a cylindrical roller.

1 6. The holder of any one of Claims 1 3 to 15, wherein the roller is mounted on a spindle.

1 7. The holder of Claim 16, wherein one end portion of each spindle of the clamping element is pivoted and the other hand can move generally towards said locating surface, thereby canting the spindle to move the clamping element generally towards said locating surface.

1 8. The holder of any one of the preceding Claims, wherein the releasing means comprises means for moving the clamping element generally towards said locating surface.

1 9. The holder of Claim 18, wherein the releasing means comprises a plunger bearing against the clamping element and projecting externally.

20. The holder of any one of the preceding Claims, for holding an object having an end locating face and two pairs of opposite sides, one pair being generally at right angles to the other pair (as seen looking at right angles to said locating surface), the holder having respective clamping and reaction ete- ments for clamping both pairs of opposite sides of the object.

21. The holder of Claim 20, for holding an object having a cuboidal part with an end locating face and four adjoining side faces at right angles to the locating face, the holder having four walls which will surround said part of the object and which encompass the locating surface.

22. The holder of Claim 20 or 21, wherein there are respective clamping and reaction elements for one pair of opposite sides and, for the other pair of opposite sides, there is one clamping element for engaging the middle of the side (as seen looking at right angles to the locating surface) and two spaced reaction elements for engaging the opposite sides.

23. The holder of Claims 1 7 and any one of Claims 20 to 22, wherein the end portion of the spindle of a clamping element associated with one side of the object crosses over the end portion of the spindle of a clamping element associated with a side generally at right angles to the first side, the releasing means moving the end portion of one said spindle generally towards the locating surface and thereby moving the end of portion of the other said spindle generally towards the locating surface.

24. The holder of any one of the preceding Claims, wherein the locating surface is formed by three co-planar pads.

25. A self-clamping holder substantially as herein described with reference to, or as shown in, Figs. 1 and 2, or Fig. 3, or Figs. 4 to 10 of the accompanying drawings.

26. The holder of any one of the preceding Claims, when incorporated in apparatus for positioning or working gemstones.