FI ELD OF THE INVENTION

This invention relates to a workpiece clamp for clamping sheet

material .

BRI EF DESCR IPTION OF THE PRI OR ART

Workpiece clamps , for example as used on punch presses for

clamping sheet material during punching , are wel l known. An example

of a recent form of workpi ece clamp is shown in figure 4 of U . S . Patent

No. 4143571.

An object of the present invention is to provide an improved

workpiece clamp.

SUMMARY OF THE I NVENTION

According to the present invention there is provided a workpiece

c lamp comprising two jaws at l east one of which is movable towards the

other to clamp a workpiece therebetween , a datum face between the jaws

which the workpiece abuts during clamping , and a sensing means

associated with the datum face to identify whether or not a workpiece is

abutting the datum face.

More particularly a wor kpiece clamp may comprise mounting means

for mounting the clamp to a workpiece support carriage , a projecting

support member carrying a lower jaw at its free end , an elongate upper

jaw pivoted on the support member and arranged at one end to cooperate

with the lower jaw to clam p a workpiece, the other end of the upper jaw

carrying a cyl inder assembly operative to cause rotat ion of the upper

jaw relative to its pivot to clamp a workpiece , a datum face between the

jaws which a workpiece abuts during clamping , and a sensing means

associated with the datum face to identify whether or not the workpiece

is in abutment with the datum face.

Preferably the datum face is on the support member and the

sensing means comprises a spring-biassed rod the free end of which , in

its position of rest , projects beyond the datum face. The other end of

the rod is arranged to cooperate with a feed-back device when the rod is

pushed rearwardly by insertion of a workpiece between the jaws to

indicate, eg : identify for a computer control , that the workpiece abuts

the datum face.

According to another aspect of the invention a wor kpiece clamp

may comprise mounting means .for mounting the clamp to a workpi ece

« support carriage, a lower jaw pivoted to the mounting means , and an

elongate upper jaw pivoted intermediate its ends and arranged at one end

to cooperate with the lower jaw to clamp a workpiece , the other end of

the upper jaw carrying a cyl inder assembly operative to cause rotation ,

of the jaw relative to its pivot to clamp a workpiece, a datum face

between the upper and lower jaws , the lower jaw including first resi l ient

means restricting pivotal movement of the lower jaw in one direction and

second resi l ient means restricting pivotal movement of the lower jaw in the

opposite direction , and sensing means associated with the datum face

to identify whether or not the workpi ece is in abutment with the datum

face.

Preferably the first resi lient means is a plate spring restricting

downward deflection of the lower jaw and the second resi l ient means

is a coi l spring resi lient upward deflection of the lower jaw.

BR I EF DESCR IPTION OF THE DRAWINGS

The invention wi l l now be described by way of example with

reference to the accompanying drawings in which:

Figure 1 is an exploded view of a preferred embodiment ;

Figur e 2 is an assembled plan view of the embodiment of figure 1

with one or two additional attachments ;

«

Figure 3 is a side el evation of figure 2; and

Figure 4 is a front elevation of the figures 2 and 3 partial ly broken

away.

DES CR IPTI ON OF THE PREFERRED EMBOD I MENT

In the drawings a workpϊ ece clamp 1 has a mounting block 2

having a groove 3 for sl idably engaging a dove-tail strip on a workpiece

carriage of a machine tool : the groove 3 being partial ly defined b y a

releasable locking strip 31. Extending from the mounting block 2 is

support member 4 consisting of two spaced arms 5 connected together

by a plate 6 and pivotal ly mounted on pivot bar 7. The support member 4

is resi l iently biassed into its normal operative position by two spring

assembl ies 8 each of which comprise a plate spring 9 permitting sl ight

downward deflection , and a coi l spring 10 permitting upward deflection,

about pivot bar 7.

Secured to the underside of the free end of support member 4 is

a lower jaw 11 having two serrated tungsten button s 12 which grip the

workpiece in use: from the drawing it wi l l be seen that the serrations on the

buttons are set at 90° to one another to provide the best grip. The upper

side of the support mem ber 4 receives a plate 13 to which the upper jaw

14 is pivotal ly connected at 15. The upper jaw 14 is elongate having a

tungsten tip 16 at one end , for cooperating with buttons 12 in gripping a

workpi ece , and a pneumatic cylinder assembly 17 at the other end.

The cyl inder assembly 17 comprises a cylinder 18 which is

adapted to receive compressed air through an inl et 19 to cause clamping

movement of the upper jaw 14. The cyl inder 18 has a reciprocal piston 20

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which includes a depending shaft 21 protruding through the bottom

of the cyl inder 18 and through an aperture 22 in the end of the jaw 14.

As seen from the drawing the upper jaw 14 is special ly contoured and

in the position of rest the end of the jaw including the cyl inder assembly

17 rests on plate 6.

The upper and lower jaws 14 and 11 define between them the

clamping area the depth of which is l imited by datum faces 23 of the

support member 4. Secured on one arm 5 of the support member 4 is

a sensing device comprising an elongate rod 24 biassed at one end by a

spring 25 so that the other end of the rod , when the clamp is inoperative ,

prot rudes beyond the associated datum face 23. The said one end of the

rod 24 has a plate 26 which serves as a sensor actuator and which cooperates

with a feed-back device 27 to the computer control for the machine tool ,

said feed-back device 27 being a proximity switch having an active surface

al igned with the actuator plate 26.

In use , in the inoperative position of the clamp , the rod 24

protrudes beyond the datum face 23 and the end of the upper jaw 14

including ihe cyl inder assembly 17 rests on plate 6. When a workpiece

is to be clamped the workpiece is pushed between the jaws 1 1 and .14 up

against datum faces 23 , this pushes back rod 24 against the force of

spring 25 causing actuator plate 26 to activate feed-back proximity device

27. Compressed air is then supplied to the cyl inder assembly 17 which

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forces piston 20 downwardly and in turn causes the depending shaft 21 to

protrude further so as to engage the plate 6. This causes the cyl inder

assembl y 17 , and that end of the upper jaw 14 , to be l ifted effecting

rotation of the jaw 14 about pivot 15 so as to clamp the workpiece between

the cooperating jaws 14 and 11. On stopping the supply of the compressed

air , the cyl inder 18 is vented and it returns to its original position by

its own weight and the piston 20 is returned by a return spring 28.

In the event that the workpiece becomes displaced from the datum

faces 23 during an operating sequence the rod 24 ceases to contact

feed-back device 27 so that a control is operative to stop the sequence.

Referring particularly to figures 2 to 4 it wil l be seen that the

workpiece clamp 1 includes a sensor actuator -28 secured to the top of

the mounting block 2 by screws 29. The sensor act uator 28 is

operative to activate a sensor (not shown) on the X-axis of a punching

machine as disclosed in detail in our copending U. K. Appl ication No.

8105597. In addition it wil l be seen that the releasable locking strip 31

is held in position by screws 32 which pass through hol es 33 in each side

arm 34 of the mounting block 2. In order to detect loosening of the locking

screws 32 in the side arms 23 a single proximity switch 35 is provided.