EP0591209B1

EP0591209B1 - Device for clamping a workpiece in a fixture, a worktable or the like

Info

Publication number: EP0591209B1
Application number: EP91919010A
Authority: EP
Inventors: Bengt Larsson
Original assignee: Hedberg Allan
Current assignee: Hedberg Allan; KELLER, LEIF
Priority date: 1990-04-26
Filing date: 1991-03-18
Publication date: 1996-05-22
Anticipated expiration: 2011-03-18
Also published as: SE465115B; DE69119788D1; DE69119788T2; WO1991016171A1; AU7775691A; SE9001510D0; EP0591209A1

Abstract

A device for clamping a workpiece (2) in a fixture or a worktable (1) comprises one or more clamping elements (4) associated with the fixture, and a disengaging tool (21) common to several such clamping elements and including at least one piston and cylinder mechanism (23, 23') actuable by a pressure medium. Each clamping element (4) comprises a slide (6) which is movable back and forth relative to a frame (5) and which is provided with a clamping member (7) that can be applied against the workpiece (2). The slide (6) is acted on by a mechanical spring (13) tending to urge the clamping member against the workpiece. A driver (9) and means (15, 16) are associated with the slide for constantly maintaining a certain minimum space between the driver and the housing. The disengaging tool (21) can be inserted in said space in order, upon actuation of the piston and cylinder mechanism of the tool, to deactivate the spring (13) and move the clamping member (7) away from the workpiece to release this from the fixture (1).

Description

The invention relates to a device for clamping a workpiece in a fixture, a worktable or the like, comprising a fixture and at least one clamping element associated with the fixture and including a slide member which is movable back and forth relative to a frame or the fixture and with which is associated a clamping member which can be applied directly or indirectly against the workpiece, said slide member being actuated by at least one mechanical spring which in an active state tends to urge the clamping member against the workpiece.

Background of the Invention

In today's engineering industry, many kinds of working operations are carried out, such as drilling, milling and the like, by means of automated program-controlled machines which do not require any manual attendance, i.e. which can operate also in the absence of attending personnel, e.g. at night or on non-working days. To such machines, the workpieces are fed clamped on fixtures, each of which often carries several workpieces. More specifically, the workpieces are clamped on the fixtures in a mounting station, from which a large number of fixtures are successively fed to the machine by means of an automatically operating conveyor. Basically, each workpiece is clamped on the fixture between a fixed abutment and a movable clamping jaw which, in prior art fixtures, is tightened either by a manually operable screw or hydraulically. None of these two techniques is however fully satisfactory. Clamping the workpieces by means of screws is a monotonous, physically tiresome work, especially when one and the same operator may have to clamp and release hundreds of workpieces every day. This work, therefore, often leads to bodily injuries, e.g. of the shoulders, back, joints and muscles. Although the technique of clamping workpieces by means of a hydraulic system integrated in each fixture is ergonomically advantageous, the fixtures become very expensive to manufacture and also require considerable maintenance. Also, it cannot be avoided in practice that a certain amount of hydraulic oil leaks out of the system, which means that an initially distinct clamping effect is successively lost.
In order to eliminate the drawbacks of the technology related above, clamping devices of the type stated by way of introduction have been developed which operate by means of a mechanical spring which in an active state holds a clamping member urged against the workpiece without the assistance of any long-term-operating hydraulic medium. Devices of this type are previously known from e.g. DE-OS 1,502,860 and 3,610,060. A serious drawback of these known clamping devices is however that the spring, in connection with the release or the clamping of a workpiece, is deactivated by means of a pressure-medium-operated piston and cylinder mechanism integrated in the device. This means that certain pressure-medium lines (both supply and return lines) must be connected to each clamping device. This is often very difficult and sometimes even impossible to do because one fixture may have a large number of clamping devices. One drawback is of course also that the overall constructional solution becomes very costly and involves extensive maintenance, since an equal number of expensive piston and cylinder mechanisms will be required as the number of clamping devices.

Object of the Invention

One object of the present invention is to overcome the above-mentioned drawbacks inherent in prior art clamping constructions by means of a device which operates only with the assistance of a mechanical spring, i.e. without any integrated piston and cylinder mechanism with associated pressure-medium lines, whereby to provide a device which is easy and cheap to manufacture and which does not require any extensive maintenance.

Brief Account of the Inventive Concept

According to the invention, the above-mentioned object is achieved by means of a device which is characterised in that the slide member is associated with a driver and means for constantly maintaining a certain minimum distance or space between the driver and the frame or the fixture, the device comprising a disengaging tool which is common to several clamping elements and which comprises at least one piston and cylinder mechanism actuable by a pressure medium, such as oil, being insertable in said space in order, by actuation of the piston and cylinder mechanism of the tool, to deactivate the spring and move the clamping member away from the workpiece for disengaging this from the fixture.
Other advantageous features of the inventive device appear from appended claims 2-6.

Brief Description of the Drawings

In the drawings,

FIG. 1: is a part-sectional schematic side view of a clamping element included in the inventive device, the clamping element being shown in an active state in which a workpiece is held clamped,
FIG. 2: is a similar side view showing the clamping element of Fig. 1 in an inactive state in which the workpiece can be disengaged from the associated fixture,
FIG. 3: is a top plan view showing a disengaging tool according to the invention,
FIG. 4: is a simplified side view of an alternative embodiment of the clamping device according to the invention,
FIG. 5: is a top plan view of the device in Fig. 4,
FIG. 6: is a side view of another alternative embodiment of a device according to the invention,
FIG. 7: is a side view of a separate clamping element included in the device of Fig. 6, and
FIGS 8-11: are side views of four further alternative embodiments of the invention.

Detailed Description of the Preferred Embodiments

Figs 1-2 schematically illustrate a fixture 1 for receiving a plurality of workpieces 2 to be positioned and held distinctly clamped in predetermined positions relative to the fixture. To this end, the fixture has for each workpiece 2 a stationary abutment 3 and a clamping element, generally designated 4, cooperating therewith. The clamping element 4 comprises a housing 5 which in this case serves as a fixed frame and in which a slide or slide-like member 6 is movable back and forth. At one end, the slide 6 has a clamping member 7 which can be applied against the workpiece 2 and which, in the illustrated embodiment, is a cylindrical, partly conical plate with a central, internally threaded hole for receiving a threaded end of the slide 6. The plate 7 can be held in place by means of a locking nut 8. At its other end, the slide 6 has a driver 9 which, in the illustrated embodiment, is a ring- or plate-shaped head on the slide end. The slide has a piston or piston-like member 10 which is here held in place by means of a locking screw 11. Between the piston 10 and a wall 12 of the housing 5, there is arranged a spring 13 which in this embodiment is a compression spring, preferably a Belleville spring washer. In its active state, the compression spring 13 tends to urge the clamping member 7 against the workpiece 2.
The rear end portion 6' of the slide 6 is comparatively thick and extends through a corresponding, relatively large opening 14 in the wall 12. The thick end portion 6' passes at a shoulder portion 15 into a thinner intermediate portion 6''. In association with the intermediate portion 6'', there is arranged a stop pin 16 projecting a certain distance into the opening 14. The spring 13 tends to urge the slide 6 to the right in the drawing. This displacement of the slide is however limited by the stop pin 16, defining one end position of the slide and, hence, always maintaining a certain minimum distance or space 17 between the head 9 and the outside of the wall 12.
The wall 12 of the housing 5 further has a transverse bore 18 accommodating a second movable stop pin 19 which is displaceable transversely of the direction of movement of the slide 6, between an inactive state, shown in Fig. 1, and an active state, shown in Fig. 2, in which it engages the intermediate portion 6'' of the slide. The displacement of the stop pin 19 can be brought about by operating a knob or lever 20 accessible on the outside of the housing 5.
The disengaging tool 21 being part of the inventive device and shown in Fig. 3 has two spaced-apart fork shanks 22, 22', each incorporating a piston and cylinder mechanism 23 and 23', respectively, operable by means of a suitable pressure medium, such as oil. More specifically, this pressure medium can be supplied to the tool through a flexible tube 24. The tool is flat and has plane front and rear faces 25 and 26, respectively. Upon actuation of the mechanisms 23, 23', their pistons can be advanced from the front face 25 of the tool, as illustrated in Fig. 2. The recess 27 defined between the two fork shanks 22, 22' of the tool has a width which is at least slightly greater than the diameter of the thickest end portion 6' of the slide 6, but at least slightly smaller than the diameter of the head 9.
The clamping device of the invention operates as follows. In its active clamping state shown in Fig. 1, the clamping element 4 urges the workpiece 2 against the abutment 3 by means of the clamping plate 7. When using a powerful spring, such as a Belleville spring washer 13, this clamping action can be performed with a considerable force which can be maintained over a long period of time without any alteration thereof. In this state, the movable stop pin 19 is removed from the slide 6, such that this is freely displaceable in the opening 14. Similarly, nor does the fixed stop pin 16 prevent displacement of the slide to the right towards the workpiece since the shoulder portion 15 is located at a certain distance from the stop pin 16 as long as the workpiece is in place.
When the workpiece 2, after completed machining, should be disengaged from the fixture, the tool 21 is inserted in the space 17 between the slide head 9 and the wall 12 of the housing 5 in the manner shown in Fig. 2. Upon actuation of the piston and cylinder mechanisms 23, 23' of the tool, whereby the pistons or piston-rod-like members thereof are extended into engagement with the wall 12, the slide head 9 will be moved away from the housing, thus retracting the entire slide. This means that the spring 13 is further compressed and that the clamping plate 7 is removed from the workpiece 2 to enable this to be disengaged from the fixture. In this state, in which the spring 13 has been deactivated in the sense that it does no longer urge the clamping plate 7 towards the abutment 3, and in which the workpiece has been removed, it is possible, once the pistons of the mechanisms 23, 23' have returned to their initial positions within the tool, to remove this from the clamping element, since the stop pin 16 always ensures a certain minimum space 17 which is at least slightly greater than the thickness of the tool, i.e. the distance between the front face 25 and the rear face 26 of the tool.
The movable stop pin 19 described above makes it possible, when desired, to lock the slide in an inactive state while the workpiece is still in place in the fixture. This locking function is especially advantageous when two or more clamping elements are used for jointly clamping a workpiece. The tool 21 may then be used for disengaging a first clamping element, whose slide is locked in the position shown in Fig. 2 in that the movable stop pin 19, by means of the operating knob 20, is moved into engagement against the intermediate portion 6'' of the slide against the action of a compression spring 20'. When the tool is thereafter deactivated, the shoulder portion 15 of the slide will lock the stop pin 19, thus prohibiting any further displacement of the slide towards the workpiece. The tool can then be shifted from the first clamping element to one or more other clamping elements which are deactivated and locked in the same way as the first-mentioned clamping element so as to completely disengage the workpiece from all the clamping elements.
Figs 4 and 5 illustrate an alternative embodiment in which the frame 5 is a lever, to which a clamping element 4 is permanently connected. As in the previous embodiment, this clamping element has a slide member in the form of rod 6 which extends through a hole (not shown) in one end of the lever 5 and which passes into a thicker portion 6' at the top side of the lever. At its free end, the rod 6 has a head 28, engaged by one end of a compression spring 13, whose opposite end engages the underside of the lever 5. Similarly, the thicker portion 6' of the slide member has a head 9 serving as a driver. In the manner described above, the disengaging tool 21 can be inserted between the driver head 9 and the frame 5 in order to compress the spring 13.
In the area between the two ends of the lever 5, there is formed an opening 29 which is elongate in this embodiment and through which a pin or bolt 30 extends, the lower end of which is fixed to the worktable or supporting structure 1 and the opposite end of which carries a washer 31 and a locking nut 32 screwed on to an upper threaded portion of the pin. By means of this arrangement, the workpiece 2 can be clamped between the worktable 1 and the end 33 of the lever 5 opposite to the clamping element 4, in that the compression spring 13, when in its active state, exerts on the lever an upwardly directed pressure which by leverage corresponds to a downwardly directed pressure on the free end 33 of the lever.
For releasing the workpiece 2, the tool 21 is inserted between the driver head 9 and the top side of the lever 5, so that the spring 13 can be compressed when the piston rods 23, 23' of the tool 21 are actuated as described above. Thus, the pressure exerted by the spring 13 on the lever is suspended, resulting in the release of the workpiece.
Since the opening 29 is elongate, the lever can be set in different positions in the horizontal direction. The lever can also be adjusted vertically by setting the locking nut 32 in different positions on the pin 30 (at the same time as washers are placed under the head 28 of the rod 6).
Figs 6 and 7 illustrate a similar embodiment in which the clamping element 4 is however arranged separate from a lever 34. As in the embodiment of Figs 4 and 5, the lever 34 is connected to a pin 30 having locking means 32 and secured to the supporting structure 1. In this case, however, the compression spring 13 is associated with an independent housing 5'. More specifically, the compression spring 13 is arranged on the upper side of a top wall 35 of the housing 5', while the thicker portion 6' of the slide member extends downwards from the underside of said top wall. In this way, the disengaging tool 21 can be inserted in the space between the underside of the top wall and the driver head 9 of the slide member in order, when required, to compress the spring 13 for releasing the workpiece 2 which is held clamped under the end of the lever 34 opposite to the clamping element 4.
Fig. 8 illustrates an embodiment in which a clamping bar 34 is adapted to retain workpieces 2 at each of its two ends. In this case, the clamping element 4 is incorporated in a housing secured to the underside of the worktable or supporting structure 1 on which the workpieces are placed. The slide member 6 is connected to the bar 34. A driver head 9 is provided on the lower end of the slide member 6, and a disengaging tool 21' can be inserted between the head 9 and the bottom wall 36 of the housing 5. A thickened portion 37 formed on the slide member and, when in a lower end position, engaging a plate 38 being part of the housing 5, ensures that the head 9 cannot move further downwards than to a position in which the space between the head 9 and the bottom wall 36 is sufficient for receiving the disengaging tool 21'.
Fig. 9 shows a similar embodiment for clamping two or more workpieces 2 by means of a common bar or plate 34. In this case, the compression spring 13 directly engages the underside of the worktable 1, while a thickened portion 6' of the slide member 6 is located on the upper side of the worktable 1. The driver head 9 is directly associated with the thickened portion 6'. In this embodiment, the disengaging tool 21 can thus be inserted at the upper side of the worktable 1, more specifically between the worktable and the driver head 9.
Fig. 10 again shows an embodiment in which the workpiece 2 is clamped by means of a lever 34. In this case, the clamping element 4 is connected to a housing 5 fixed to the worktable or supporting structure 1, the pin or column 30 forming the fulcrum of the lever being also connected to the housing.
Fig. 11, finally, shows a clamping device comprising an abutment 3 fixedly mounted on the worktable 1 and a holder, generally designated 39, which is movable relative to the abutment, although lockable in different setting positions relative thereto. A frame 5 is fixedly mounted on the holder 39, while a displaceable member disposed thereon is designated 40. The compression spring 13 is arranged between the frame 5 and the displaceable member 40, the slide member 6 projecting with a thickened portion 6' from the side of the frame 5 opposite to the displaceable member or clamping jaw 40. A head 9, serving as driver, is provided on the slide member 6, as described above. In the state shown in Fig. 11, the compression spring 13 urges the clamping jaw 40 against a workpiece 2 disposed between the clamping jaw and the abutment 3. When the workpiece is to be released, the disengaging tool is inserted in the space between the head 9 and the frame 5, and the compression spring is deactivated by means of the piston and cylinder mechanisms of the tool.
At the end of the slide member 6 opposite to the head 9, there is provided a further head 41 accommodated in a cavity in the clamping, jaw 40 and preventing unintentional release of the clamping jaw from the rest of the holder.

Possible Modifications of the Invention

It goes without saying that the invention is not restricted only to the embodiments described above and illustrated in the drawings. Thus, the clamping element can be designed so as to clamp the workpiece by a tractive force instead of a pressure as illustrated in the drawings. Whether the required clamping force is a tractive force or a pressure exerted on the workpiece, it can be produced either by means of a compression spring, as shown in the drawings, or by means of a tension spring, although the former alternative is preferred in practice, since the force exerted by a compression spring normally exceeds that of a tension spring. Instead of a fixed stop pin integrated in the spring housing, it is possible, as shown in Figs 4-11, to use other means for ensuring a certain minimum distance between the driver means of the slide member and the housing. Further, the clamping member 7 need not be a plate, but may be designed in many other ways. Thus, the clamping member may be e.g. a fork, a ball or the like. In the extreme case, the clamping member may simply be a flat end surface of the slide 6. The driver 9, too, may have a shape other than that of an annular head on one end of the slide. In this context, it should be pointed out that the space in which the disengaging tool is insertable may be directly defined by components other than the housing or frame itself, e.g. by a support plate connected to the housing. It should be noted that the invention can be used not only in connection with fixtures of the type stated by way of introduction, but also in connection with other optional supporting structures, such as workbenches.
It should further be observed that the illustrated disengaging tool according to the invention can be modified in many different ways. In the case of a fork-shaped tool, this may thus have more than two (diametrically opposed) piston and cylinder mechanisms, e.g. three or even more, which are suitably distributed along the recess defined by the fork shanks. As shown in the embodiment of Fig. 8, it is also possible to use a disengaging tool with only one piston and cylinder mechanism.

Claims

A device for clamping a workpiece in a fixture, a worktable or the like, comprising a fixture (1) and at least one clamping element (4) associated with the fixture (1) and including a slide member (6) which is movable back and forth relative to a frame (5) or the fixture and with which is associated a clamping member (7) which can be applied directly or indirectly against the workpiece (2), said slide member being actuated by at least one mechanical spring (13) which in an active state tends to urge the clamping member (7) against the workpiece (2), characterised in that the slide member (6) is associated with a driver (9) and means (15, 16) for constantly maintaining a certain minimum distance or space (17) between the driver (9) and the frame (5) or the fixture, the device comprising a disengaging tool (21) which is common to several clamping elements and which comprises at least one piston and cylinder mechanism (23, 23') actuable by a pressure medium, such as oil, being insertable in said space (17) in order, by actuation of the piston and cylinder mechanism of the tool, to deactivate the spring (13) and move the clamping member (7) away from the workpiece (2) for disengaging this from the fixture (1).
Device as claimed in claim 1, characterised in that the driver is a head (9), e.g. a ring or plate, projecting from the slide member (6).
Device as claimed in claim 1 or 2, characterised in that the disengaging tool (21) has two spaced-apart fork shanks (22, 22') provided with piston and cylinder mechanisms (23, 23') which can be applied on each side of the slide member (6).
Device as claimed in any one of the preceding claims, characterised in that the clamping element (4) comprises a movable stop (19) serving, as desired, to temporarily retain the slide member (6) in the state where it is disengaged from the workpiece (2), also when said tool (21) is removed from the clamping element, with the workpiece remaining in the fixture.
Device as claimed in any one of the preceding claims, characterised in that the clamping member is a plate (7) provided on one end of the slide member (6).
Device as claimed in any one of the preceding claims, characterised in that the spring is a compression spring, such as a Belleville-type spring washer (13), disposed between a wall (12) of the housing (5) and a piston or piston-like member (10) on the slide member (6).