US 3027155 A
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Description (OCR text may contain errors)
March 27, 1962 D. R. PATERSON 3,027,155
MEANS FOR RELEASABLY CLAMPING ARTICLES Filed Dec. 21, 1959 k//ll/l/l/IIIIIIII/I/IIIII/A Fig .3 2 5 g V /A/VNTO/2 @MWW A TTOP/VEY 3,927,155 MEANS FOR RELEASABLY CLENG AEi'illiILES David Robert Paterson, London, England, assignor to Transfer Tools Limited, London, England, a company of Great Britain Filed Dec. 21, 1959, Ser. No. 861,044 Claims priority, application Great Britain Dec. 23, 1958 7 Claims. (Cl. 269--32) This invention relates to means for releasably clamping articles, such as workpieces to be held in a jig or fixture or on the table of a machine tool, of the kind (hereinafter referred to as the kind specified) comprising a clamping jaw movable towards and away from a clamping position by the straightening and breaking, respectively, of a toggle having the free end of its one link pivoted on the jaw and the free end of its second link engaged with a fixed pivot and an actuating member, e.g. a fluid pressureoperated piston, movable in one direction to cause straightening of the toggle and in an opposite direction to cause breaking of the toggle. In such means as previously proposed, the actuating member has been pivotally connected to the knee joint of the toggle so that during the operation of the means this connection has been constrained to move in an arcuate path. When, as is usual, the actuating means comprises a piston working in a cylinder adapted to be supplied with fluid under pressure, it has been necessary to mount the cylinder so that it may oscillate through a small angle in order to accommodate the variation in the angular disposition of the piston rod occasioned by the arcuate motion referred to.
It is an object of the present invention to provide an improved clamping means of the kind specified which shall be such that the actuating member will only have to move in a rectilinear path so that when it comprises a fluid pressure-operated cylinder and piston arrangement, the cylinder may be mounted in a fixed position. The improved clamping means also affords certain other advantages. According to this invention, in means of the kind specified, the actuating member is arranged to act on the centre point of the central or connecting lever of a Watt Straight Line Motion, one of the pivoted links of this motion is arranged to operate extending means for increasing the effective overall length of the toggle during that motion of the pivoted link which is produced by movement of the actuating member in the toggle-straightening direction, and the central lever of the motion is linked to the second link of the toggle, the arrangement being such that the first part of the travel of the actuating member in the direction for straightening the toggle will produce a rapid straightening motion of the toggle adapted to bring the jaw into an initial clamping position, a subsequent par-t of this travel will not substantially change the angular relationship of the links of the toggle but will cause the extendin means to increase the effective length of the toggle, and the final part of this travel will produce a final straightening of the toggle to apply full clamping pressure to the jaw.
It is preferred that the initial clamping position shall correspond to the engagement of the clamping jaw with an article, such as a workpiece, of the maximum permitted size, the maximum increase in the effective length of the toggle which is obtainable corresponding to the movement of the clamping jaw from this initial position to a position corresponding to the engagement of the clamping jaw with an article or workpiece of the mini mum permitted size. The increase in the effective length of the toggle may be brought about by arranging for some lost motion in the knee joint of the toggle and providing means actuatable by the pivoted link of the straight line tnt ice
motion for bodily displacing the one link of the toggle with respect to the second link thereof in the direction for moving the clamping jaw towards the final clamping position. Such means may comprise a cam element adapted to co-operate with a cam surface formed on the knee joint end of the first link of the toggle, and this cam element is preferably actuated from the pivoted link of the straight line motion through a friction or spring drive which is adapted to slip or yield when the resistance to motion encountered by the cam element exceeds a predetermined maximum.
It is preferred to provide means whereby the length of the first link of the toggle may itself be adjusted to a pre-set value in order to render the clamping means according to the invention suitable for use with workpieces of differing nominal sizes.
In order that the invention may be clearly understood, one construction of a fluid pressure-operated releasable clamping means according thereto will now be more fully described with reference to the accompanying drawings, in which:
FIG. 1 is a longitudinal section showing the clamping jaw in its retracted position,
FIG. 2 is a similar view showing the parts in the position they occupy when the clamping jaw has been moved to the initial clamping position,
FIG. 3 is a similar view showing the parts in the position they occupy when the effective length of the toggle has been increased to the maximum extent, and
FIG. 4 is a similar view showing the clamping jaw in its final clamping position. The example illustrated is intended for mounting on the table of a machine tool at a location such that the clamping jaw may engage a workpiece 1 and secure it to the table (in conjunction with other such clamping means, if required) while machining operations are performed on the workpiece.
The clamping means comprises a frame member 2 adapted to be secured to the table and having two side cheeks 2a in which are journalled the ends of pivots 3, 4 and 5 extending between them. The frame member rigidly supports a horizontally disposed cylinder 6 in which a piston 7 is movable to and fro by admitting compressed air to each end of the cylinder in turn under the control of suitable manually or automatically operated valves, the ports for the inlet and exhaust of the compressed air and the valves being of known construction and therefore not illustrated.
Secured to the piston 7 is a piston rod d which passes through an appropriately packed opening in the cylinder end and an aperture 9 in the frame member 2 to be pivotally attached at 10 to the central lever 11 of a Watt Straight Line Motion of which the pivoted links 12 and 13 are articulated at their one ends to the lever 11 at 14 and 15, respectively, the other ends of the links being mounted on the respective pivots 4 and 5. The pivot 19 is disposed midway between the articulations 14 and 15 and the effective lengths of the links 12 and 13 are equal so that, in the known manner, the pivot It will be constrained to move in a substantially straight line as the central lever 11 is displaced in the horizontal direction by motion of the piston 7 in the cylinder 6.
The central lever 11 is of somewhat triangular shape, the side extending between the articulations l4 and 1-5 constituting the base of the triangle, and has pivoted to its apex, at 16, the one end of a link 17 of which the other end is engaged with a pivot disposed part-way along the length of the second link 29 of a toggle i9, 243. The first link 19 of the toggle is pivotally attached atone end, at 21, to the upper end of a carrier 22 which is pivotable about the pivot 3 and has secured on its face directed towards the workpiece 1 a replaceable clamping jaw 23. The other end of the link 1? has a pivot pin 24 secured therein at a short distance from its extremity the edge of which is shaped as a cam surface 25. The second link of the toggle 19, 2%, is pivoted at one end on the pivot 4 and has a longitudinally extending slot 26 formed near its other end to receive the pivot pin 24 carried by the other link 19.
Also pivotally mounted on the pivot 4 is a compensating arm 27 which is frictionally coupled to the pivoted link 12 of the straight line motion 11, 12, 13, for example by means of an interposed friction washer (not shown). An abutment pin 28 is secured in a tailpiece of the arm 27 so that it is in contact with the adjacent edge of the link 12 when the parts are in their initial position (shown in FIG. 1).
The free end of the compensating arm 27 is shaped to a cam surface 29 adapted to cooperate with the cam surface on the end of the first link 19 of the toggle. The shapes of these cam surfaces are such that when the toggle is brought, in its straightening motion, almost to the links-in-line position with the pivot pin 24 at the end of the slot 26 nearer to the pivot 4, the cam surfaces will be in contact with each other and the point of contact on the surface 29 (which is eccentrically disposed with respect to the pivot 4) will be towards that end of this surface which is nearer to the pivot 4 than the other end. The motion of the arm 27 produced during the clamping operation tends to move the larger radius part of the surface 29 into engagement with the surface 25 which latter is substantially concentrically disposed with res ect to the pivot pin 24.
The side cheeks 2a of the frame member are bridged at the upper edges by a plate 3% which carries an abutment pin 31 disposed so that it will prevent the toggle 19, 20 from passing through its dead-centre or links-in-line position. Also, a roller 32 is mounted on the pivot or articulation 15 to cooperate with an appropriately curved side edge 27a of the arm 27, the roller engaging this edge during the first part of the motion of the link 12 in the clamping operation so that the arm 27 is positively constrained to move with the link up to the stage at which the cam surfaces 25 and 29 are just about to engage each other. This roller will also ensure that the arm 27 returns correctly into its original position during the clampreleasing operation, as indicated below.
In the operation of the clamping means described, the following steps occur.
The workpiece i is placed in position on the table of the machine tool while the clamping jaw 2-3 is retracted, as shown in FIG. 1. Air under pressure is admitted to the outer end of the cylinder 6 to force the piston 7 to travel towards the right. During the first part of this travel the central lever ill is displaced bodily towards the right while at the same time rotating about the pivot in the anti-clockwise direction (as sec-n in the figures). Consequently, the motion imparted to the link 1 17 produces a rapid displacement of the second link 2i"? of the toggle about the pivot 4 in the direction for closing the clamping jaw 23 on to the workpiece i, the compensating arm 27 being positively displaced meat ....le by the link 12 due to the provision of the abutment pin 28 and the roller 32. As the toggle approaches the dead-centre position, the roller 32 leaves the end of the edge 27a of the arm 27 and the cam surface 29 engages the cam surface 25, the pivot pin 24 heirs" then at the end of slot 26 nearer to the pivot 4. The position of the clamping jaw 25 (see PH 2) is such that it would just be in engagement with the workpiece if this is of the maximum permitted size.
Further motion of the piston 7 towards the right causes the central lever 11 to move bodily towards the right but also to rotate about the pivot iii in a clockwise direction so that the resultant motion of the pivot 16 is effected substantially concentrically with relation to the pivot 18. Consequently, the link 17 swings about this pivot 18 Without moving the links 19, 29 any nearer to the dead-centre position. At the same time, however, the further swinging motion of the link 12 drives the compensating arm frictionally in the sense for causing its cam surface 29 (by engagement with the cam surface 25) to displace the link w bodily in the clamp-closing direction. When the clamping jaw encounters the workpiece, the resistance to further motion of the link 19 thereby occasioned causes the frictional drive between the link 12 and the arm 27 to slip, the length of the slot 26 being such as to accommodate all the permissible variations in size of the workpieces.
The subsequent final motion of the piston 7 towards the right causes such a displacement of the pivot 16 as will cause the link 17 to complete the movement of the toggle links to the dead-centre position, the cam surface 25 on the link 19 rolling on the cam surface 29 on the arm 27 and the point of engagement between these surfaces being located on the line joining the axes of the pivots 4 and 21.
It will be appreciated that the arm 27 is forced to travel a little farther by the rolling of the surface 25 on its cam surface 29 so that a very high clamping pressure on the workpiece is generated due to the slight additional displacement of the link 19 which is thus caused. Moreover, the stress is transmitted entirely through the link 19 and the arm 27 to the pivot no stress being imposed on the pivot pin 24.
Release of the clamp is effected by supplying air under pressure to the right hand end of the cylinder 6 to cause the piston 7 to move towards the left. The first portion of this movement causes the link 17 to break the toggle and the motion of the link 12 causes the arm 27 to move with it (due to the friction drive) until the lower end of the leading edge of the arm 27 encounters the roller 32. Further motion of the arm 27 is then only possible as permitted by the motion of the roller until the link 12 strikes the abutment pin 28 and from then on the arm 27 is constrained to move with the link 12 back towards its initial position. The parts return to their initial position (shown in FIG. 1) passing through the various intermediate positions shown in FIGS. 3 and 2.
Adjustment of the position in which the clamping jaw wil engage a workpiece of the maximum size may be effected by making the link 19 adjustable in length. For example, its end portions may be constructed as nut elements engaged with the respective oppositely screwthreaded ends of an intermediate portion which is rotated in order to vary the effectively length of the composite link.
In some cases the drive between the link 12 and the arm 27 may be effected through a pre-stressed spring instead of a friction element, the spring yielding when the excessive resistance to the movement of the arm is encountered.
It is desirable to provide for adjustment of the final clamping movement of the toggle and, to this end, the angular movement of the link 2%), as it moves between the position shown in FIG. 3 and the final clamping position shown in FIG. 4, may be either increased or reduced by either reducing or increasing, respectively, the
distance between the pivots l6 and 18 for the link 17. For example, the central lever it may be formed with three apertures for receiving the pivot E6 each aperture being at a different distance from the pivot 14.
In some cases the arm 27 may be replaced by a toggle arm which would extend in length during the period in which the arm 27 normally would be operative to displace the link it") until contact had been made between the clamping jaw and the workpiece. The toggle arm would take the full clamping pressure (instead of the arm 27) and the extension of the toggle arm would be derived from the movement of the link 12 as before.
What I claim is:
1. Means for releasably clamping articles comprising a clamping jaw movable between an inoperative position and an operative position, a toggle having provision for lost motion in the connection between its links and connecting said jaw to a fixed abutment, the toggle being in broken condition when the jaw is in the inoperative position and in straightened condition when the jaw is in the operative position, an operating lever, an actuating link connecting sai lever to a link of the toggle, actuating means adapted to impart translatory motion to said lever between a toggle-broken position and a toggle-straightened position, the translatory motion of the lever towards its toggle-straightened position impartiug toggle-closing motion to said actuating link, means constraining said lever to oscillate during its translatory motion towards the toggle-straightened position so that towards the end of this motion the oscillatory and translatory motions of the lever will have opposite and substantially equal efiects upon the actuating link, a dwell in the straightening of the toggle thereby resulting, extending means capable when moved through an operative position of increasing the effective length of the toggle, and means operated from said actuating means to drive said extending means through its operative position during the dwell in the straightening of the toggle, said drive means being arranged to become inoperative for displacing the extending means upon the latter encountering a predetermined resistance to its displacement.
2. Means as claimed in claim 1, in which the actuating means is a reciprocatory member, the means constraining the lever to oscillate is a pair of links of equal length each pivoted at one end to a fixed part and at the other end to a respective end of the lever, said reciprocating member and said lever being pivotally connected to each other by a pivot disposed midway between the ends of the lever.
3. Means as claimed in claim 2, in which the actuating link is connected to the lever by a pivot spaced from the line joining the ends of said lever.
4. Means as claimed in claim 1, in which the extending means, when moved through its operative position, displaces one link of the toggle with respect to the other link thereof in the direction for moving the clamping jaw towards its operaitive position.
5. Means as claimed in claim 4, in which the extending means comprises a cam element and said one link of the toggle is formed with a cam-engaging surface on its end adjacent to said other link.
6. Means as claimed in claim 5, in which the cam element of the extending mean is pivotally mounted on the fixed abutment to swing about the same axis as that link of the toggle connected to said abutment.
7. Means as claimed in claim 1, in which said drive means is operated from said actuating means through a friction drive adapted to slip when the extending means encounters the predetermined resistance to its displacement.
References Cited in the file of this patent UNITED STATES PATENTS 1,766,812 Damerell June 24, 1930 1,812,959 Judd July 7, 1931 1,973,801 Dustan Sept. 18, 1934 2,039,041 Wall Apr. 28, 1936 2,567,436 Lampe Sept. 11, 1951