GB2327898A - Clamping arrangement - Google Patents

Abstract

An arrangement for clamping workpieces to a work table comprises at least one static clamp 1, and at least one movable clamp 2 which can be both manually and mechanically actuated. Preferably, the or each movable clamp 2 is moved manually within a framework of T-shaped slots 3,4 for a course adjustment using an adjustable screw mechanism (not shown), followed by a fine mechanical actuation. Preferably, this mechanical actuation uses a wedge 8 and shoulder 5,7 cam mechanism which operates indirectly on the jaw 6 on the or each movable clamp 2. In this case, the wedge 8 is driven downwards by a hydraulic piston and cylinder combination 20, thus moving the jaw 6 in a direction perpendicular to the downward force of the wedge 8. This hydraulic piston and cylinder combination 20 is preferably in the form of a cartridge which can be inserted into, and removed from, the or each movable clamp 2. Preferably a plurality of clamps 1,2 are located on the work table, so that a large workpiece can be retained, and each movable clamp 2 can occupy any one of a number of discrete locations on this work table.

Description

SECURING SYSTEM The invention relates to a system for securing workpieces and tool for use in the system.

Workpieces, when being machined, are often held in a machine vice so that they can be maintained securely in place and positioned accurately. A conventional machine vice comprises a static and a moving jaw, and the workpiece is secured between the jaws. The vice may be secured to a work table which can be moved relative to the machine tool so that the workpiece can be accurately positioned for machining. In the vice the moving jaw may be adjusted by screw means so that it can be tightened against the workpiece and the workpiece can be secured between the moving jaw and static jaw.

If a larger workpiece is to be machined it may be convenient to use separate static and moving jaws and to secure these independently to the work table, so that, in effect, the work table and moving and static jaws form the vice. In this case the static jaws, or in some cases several static jaws will be located and secured on the work table to engage one side of the workpiece. The moving jaws will then be located and secured on the work table so that they are in a position to enable them to engage another side of the workpiece. The moving jaws are then manually adjusted so that they engage the workpiece and clamp it effectively between the static and moving jaws. The workpiece is then held between the jaws and securely on the work table, and the work table can be moved so that the workpiece is correctly located in relation to the tool which is to be used for machining the workpiece. The moving jaw consists of a base, which is secured onto the worktable, and ajaw member which can be manually adjusted relative to the base by screw means.

In one variation of this type of workpiece securing system, the work table is in the form of a planar platform with channels cut into the top (plane) surface of the platform. The static and moving jaws can be located onto the work table by having feet which slot into the channels. In this way the jaws can be located more precisely. They can be secured to the work table by bolts which are secured into the channels, for example by having channels with an inverse "T" crosssection and a complementary head on the bolt which engages the inner surface of the channel.

A nut can then be tightened on the shank securing the jaw to the worktable.

The work table can have two sets of channels in perpendicular directions across the surface of the work table together forming a grid which permits the jaws to be placed in a wide choice of positions.

Although such workpiece securing systems have many advantages, because of their versatility, they are often relatively slow to use, because.of the need for manual adjustment and fastening.

Mechanically powered adjustable securing means can be used, but are generally cumbersome and either do not have the versatility of manual securing systems or are very expensive.

Accordingly the present invention provides a workpiece securing system comprising a work table and static and detachable manually adjustable moving jaws (referred to below as "clamps") characterised in that the manually adjustable jaw clamp or clamps have integral mechanically powered adjusting means.

Preferably the moving jaw clamp comprises a jaw member and a base on which the jaw member is movably secured. The base is adapted to be secured to the work table, and the jaw member to be moved on the base. Preferably the integral unit has a footprint no greater than that required to secure the base firmly to the work table, and is no higher (viz in its dimension perpendicular to the work table) than the height of the jaw member from the work table.

Conveniently the axis of movement of an axially actuated mechanical actuation member is perpendicular to the plane of the work table, and therefore perpendicular to the axis of movement of the jaw. Preferably also the jaw movement of the clamp is actuated indirectly, through a cam mechanism. An example of such a cam mechanism is a linear cam for example formed by having a shoulder element on the base of the clamp and a shoulder element on the reverse of the jaw member, so that the two shoulder elements face each other and together form a valley, and providing in the gap between the shoulder elements, a wedge element each of the two operative faces of which engage one of the shoulder elements. In this way, when the wedge is force down into the valley, the two shoulder elements are forced apart and the jaw member is moved axially in a direction away from the shoulder forming part of the base.

Conveniently the wedge element can be drawn down into the valley by actuating means secured between the wedge element and the base of the clamp. Preferably the actuating means comprise two elements which operate together, the first being a manually operated actuating means and the second being a mechanically operated actuating means. Conveniently the mechanically operated actuating means can be in the form of a hydraulic cylinder and piston arrangement mounted between the wedge element and the base of the base unit. When hydraulic pressure is applied to the cylinder it causes the piston to be drawn into the cylinder so that the wedge is drawn into the valley.

Preferably the manual actuating means is in the form of a screw mechanism, for example a bolt the head of which secures against the wedge element and the shank of which is secured in the shank of the piston. The piston must be secured against rotation, and preferably this is achieved by having a slot cut transversely in the piston, preferably at it base (distal portion from the shank) and a pin, secured in the cylinder which engages the piston against rotation. The piston may also be prevented from rotating by other means such as axially directed splines engaging with part of the inner surface of the cylinder, or by use of a non-circular cross section. However, use of a slot is preferred as it is simple and permits the use of circular seals between the cylinder and the piston.

Preferably the piston shank has an internal axial thread which matches that on the shank of the bolt, so that when the bolt is tightened the bolt shank is drawn into the piston shank. In this way the clamp can be manually adjusted at the same time as having mechanically powered adjustment. (In this context adjustment is used to include tightening the clamp to its clamping pressure).

Preferably the cylinder in which the piston moves is a discrete unit which can be removed from the clamp unit, so that a manually operated clamp can be converted to an integral manual and mechanically operated clamp simply by replacement of unit into which the bolt shank secures in the manual unit by the cylinder and piston unit. Conveniently the cylinder unit is a generally cylindrical insert, comprising a cavity for accepting the piston, and on its exterior, seals on either side of the hydraulic pressure entry port. In this way the unit can be slid into an existing manual clamp unit, with an appropriate hydraulic inlet provided, and be converted into a mechanically powered unit. Preferably in such a unit, means are provided to prevent rotation of the cylindrical insert within the cavity in the base. Conveniently such means comprise a slot in the base of the cylinder and corresponding abutting section ofthe base, and a tenon inserted into the slots so that it engages both slots and prevents rotation of the cylinder.

Preferably, the mechanically powered movement in such a unit is limited to the same or less than the manually actuated adjustment, so that the size of an actuating mechanism of the required power can effectively be inserted within an existing size of clamping unit. Preferably therefore the manual means is used for adjustment to broadly the correct clamping position and then the mechanically powered means is actuated to secure the workpiece in position.

The base unit may be secured to the work table having channels as described above. Preferably the clamp has a foot which engages the channel, so as to permit more precise location of the clamp, and to prevent unwanted movement of the clamp during use. Further preferably, the foot has a tread which has a repeating profile along the length of the foot (along the axis of the channel), and the channel has a complementary profile, so that the tread and the channel can be matched at regular discrete intervals along the axis of the channel. In this way the clamp can be positioned very much more accurately at specifically indexed locations. Preferably the complementary profile is in the form of a removable base piece, which slots into the channel and can be located at indexed positions in the channel, for example by having a cross piece which engages transverse channels on the work table. Preferably the period (repeat distance) of the profiles is less than 5mm, preferably 2 to 4mm, particularly around 3mm. In this way the clamp can be positioned at discrete intervals every 3mm or so along the channel. This makes positioning of the clamp very much easier, and very precise positioning possible without detailed measurements being made, and the location of the clamp when fastened to the work table very much more secure. A convenient form of profile is in the form of a pair of combs, or more particularly a series of transverse rectangular cross section slots and ridges. The slots on one piece engage the ridges on the other and vices versa, and the relative position of the two pieces can be adjusted by discrete amounts equal to the distance between the slots.

In clamps according to the present invention the movement ofthejaw due to the mechanically powered actuator can be less than the period of the profile on the foot. Preferably the jaw movement resulting from mechanically powered actuation is less than 3mm, preferably about 2mm. The advantage of the clamp of the present invention is that the manual adjustment can be made to within the stroke of the mechanically powered actuator and when all the clamps have been set up they can be actuated mechanically to secure the work piece. In this way after the initial set up, workpieces can be secured and released very rapidly and with a great deal of precision.

Preferably the hydraulic means used to actuate some of the clamps of the present invention is detachable from the clamp unit. Preferably it is in the form of a pressurised air driven booster which can use a standard workshop airline to generate hydraulic pressures of up to about 350 bar.

Preferably the activation of the hydraulic pressure creates a linear clamping force of more than 250kg force, preferably more than 500kg, particularly in the region of 1000kg.

The invention is further described, by way of example, below. It will be appreciated that there are numerous additional means by which the invention can be put into effect.

Figure 1 is a perspective view of a work table with a number ofjaws mounted on it.

Figure 2 is a cross-sectional view of a moving jaw clamp with the cylinder and piston combination removed.

Figure 3 is a cross-sectional view of the cylinder unit of the moving jaw clamp.

Figure 1 shows a worktable with clamps fastened onto to the table. The clamps, 1, are static jaw clamps, and 2 are moving jaw clamps. The work table has a grid of channels, 3 and 4, a right angles to each other. Channels in one direction have an inverse "T" cross-section.

Each of the static jaw clamps, 2, consists of a jaw piece mounted on a base. The base has a lateral slot along each side to accept side clamps.

The securing system, which is not shown in detail in the figures, is as follows. The side clamps each have two recessed holes (at 37.5mm centres) to accept socket headed capscrews which screw into "T"-nuts. The "T"-nuts are insered into the "T"-slot channels and the side clamps can thus sllide into the preferred clamping position along the fixed jaw clamp and be tightened to secure the fixed jaw clamp to the work table. In addition the base of each static clamp has perpendicular (cross) channels cut in its underside. Four foot-pieces are inserted into the channel.

Part of each foot-piece extends below the surface of the base and is adapted to fit closely into the channel so as to locate the base accurately relative to the channel. The base can be located in the channel by reference to the grid of channels by having the footpieces in a cruciform arrangement so that two footpieces lie in one channnel on the work table and the other two lie in a perpendicular channel. The bolts passed through the holes in the side clamps are then secured into the channels to fasten the static clamp in place.

The moving jaw clamp is of a similar overall design to the static jaw clamp and the clamp is fastened to the work table using sideclamps also in the same way. However, one or a pair of foot-pieces is inserted into the channel in the underside of the base. Part of the foot-piece extends below the surface of the base and is adapted to fit closely into the channel in the work table so as to locate the base accurately relative to that channel. In addition one ofthe foot-pieces may have a tread which in the form of a number of transverse slots (alternating with ridges) of rectangular cross-section, so that the base of the foot-piece looks castellated. A complementary base piece can then be placed in the channel. The foot-piece and complementary base piece match together when the ridges on one piece slots into the slots on the other and vice versa. In this way the foot-piece and base piece fit together in a complementary manner in a number of discrete axial positions. In practice a distance between slots of 3mm can be used. The base piece can be located in the channel by reference to the grid of channels, for example, by having a transverse cross arm which matches the transverse channels. The moving jaw clamp, with its base unit and footpiece is then located in a channel in the worktable over the base piece. The foot-piece only fits into the base piece at intervals of 3mm axially and it is therefore easy to locate the clamp precisely on the work table. Bolts passed through the holes in the side clamps and the base is then secured into the channels to fasten the moving jaw clamp in place.

On the base there is mounted a fixed shoulder member, 5. The reverse face ofthejaw member, 6, has a further shoulder member, 7. The two shoulders face each other and together form a "V" shaped valley. A wedge member, 8, is placed between the two shoulders, 5 and 7, such that when the wedge member is forced down into the valley, the shoulders are forced apart. In this way the jaw member of the moving jaw clamp is forced away from the fixed shoulder.

The wedge member has a recessed hole, 9, adapted to fit a suitable bolt head, 10, and a bolt, 11, is passed through the hole and supported in the hole by a conventional spherical surface washer, 12, so that the bolt can rotate to a limited extent transversely relative to the wedge. The bolt has a conventional hexagonal recess, 13, in its head for a tightening tool.

The shank of the bolt, 11, is then secured into the piston of a hydraulic actuator, 20, which is mounted in the base, 21, of the clamp. The piston is of circular transverse cross-section, and "T" shaped cross-section along its axis. The leg (the piston shank), 22, of the "T" has an internal thread of the same dimensions as the shank of the bolt, and the bolt can be tightened and loosened into it. The top ofthe "T", 23, provides the piston surface, and seals, 24, 25, 26, 27 seal the piston against the cylinder, 28. A hydraulic line, 29, connects with the interior of the cylinder. In use, when the hydraulic pressure is applied, the "T" shaped piston is pushed downwards and at the same time pulls the bolt downwards. This pulls the wedge into the valley between the shoulders and forces the two shoulders apart. By forcing the shoulders apart the jaw member is moved relative to the base and towards the workpiece, so securing the workpiece. The moving jaw member, 6, is secured, but still moveable, by screws (not shown) passing through the lower part of the fixed shoulder, 5, and threaded into the lower part of the back of the moving jaw member, 6. A compression spring (not shown) is mounted around the shank of each of the screws, so that, on release of the hydraulic pressure the moving jaw member is forced backwards (inwards) and the wedge and piston are forced upwards.

A transverse slot, 30, is provided in the base of the piston, into which a pin (not shown), which is secured in the cylinder body, engages, so as to prevent axial rotation of the cylinder. This is required in use so that the bolt can be manually tightened to the desired position, without the piston rotating.

For convenience the cylinder is a separate component from the base. Seals, 31 and 32, are provided so that the cylinder seals against the base unit, 20, and the hydraulic line can be connected directly to the base unit. In practice it is convenient to make the cylinder with a circular cross section so that the seals can be easily fitted. A slot, 33, is provided in the bottom of the cylinder unit, and a corresponding slot in the base unit (not shown), and a tenon (not shown) fits into the slots to prevent rotation of the cylinder in the base unit. The cylinder has a flange, 34, around the base to prevent the cylinder from being drawn through the body of the clamp when the cylinder and piston arrangement is actuated and a downward force applied on the wedge.

Because of the compact space available for the cylinder and piston, movement of the piston is limited. In use therefore the jaw is manually adjusted using the bolt until it is close to the workpiece. Each jaw is adjusted in this way. The workpiece is then secured by application of hydraulic pressure which moves the jaw the additional distance necessary to secure the workpiece. In addition, because the final movement is made using hydraulic pressure, the force against the workpiece can be controlled much more accurately, so that there is more consistency between operations and less risk of harm to the workpiece, by either being too lightly or heavily fastened.

Claims (13)

CLAIMS:

1. A workpiece securing system comprising a work table and at least one static clamp and at least one manually actuated moving jaw clamp adapted to be secured to the worktable, characterised in that the moving jaw clamp has integral mechanically powered actuating means.

2. A workpiece securing system according to claim 1, in which the actuating means operates indirectly on the jaw through a cam mechanism.

3. A workpiece securing system according to claim 2, in which the cam mechanism is in the form of a wedge and shoulder cam.

4. A workpiece securing system according to any of claims 1 to 3 in which the thrust of the mechanical and powered actuating means is axial and the axis of jaw movement is broadly perpendicular to the axis of the thrust of the actuating component.

5. A workpiece securing system according to any of claims 1 to 4 in which the mechanically powered actuating means comprises a hydraulic cylinder and piston combination and thc manually actuated actuating means comprises an adjustable screw means integral with the hydraulic cylinder and piston combination.

6. A workpiece securing system according to claim 5 in which the hydraulic cylinder and piston combination is in the form of a cartridge which can be inserted into and removed from a moving clamp.

7. A workpiece securing system according to any of claims 1 to 6 in which the moving jaw clamp has indexing means to the surface of the work table, such that the clamp is indexed to a number of discrete locations on the work table in the direction of movement of the jaw.

8. A workpiece securing system according to claim 7 in which the movement of the jaw resulting from actuation of the mechanically powered actuation is less than the distance between the indexed locations.

9. A moving jaw clamp for use in a workpiece securing system according to any of the preceding claims.

10. A workpiece securing system substantially as described herein with specific reference to the drawings.

Amendments to the claims have been filed as follows 1. A workpiece securing system comprising a work table and at least one static clamp and at least one manually actuated moving jaw clamp adapted to be secured to the worktable, characterised in that the moving jaw clamp is relocatable and has integral mechanically powered actuating means.

2. A workpiece securing system according to claim 1, in which the moving jaw clamp comprises a base and ajaw member, and the footprint of the integral unit ofjaw member and base is no greater than that of the base.

3. A workpiece securing system according to either of claims 1 or 2, in which the actuating means operates indirectly on the jaw through a cam mechanism.

4. A workpiece securing system according to claim 3, in which the manually actuation of the moving jaw is also through the cam mechanism.

5. A workpiece securing system according to either of claims 3 or 4, in which the cam mechanism is in the form of a wedge and shoulder cam.

6. A workpiece securing system according to claim 5, in which the shoulder cam forms the rear of the base, the actuating means (apart from the shoulder cam) lies between the shoulder and the jaw member.

7. A workpiece securing system according to any of claims 1 to 6 in which the thrust of the mechanical and powered actuating means is axial and the axis of jaw movement is broadly perpendicular to the axis of the thrust of the actuating component.

8. A workpiece securing system according to any of claims 1 to 7 in which the mechanically powered actuating means comprises a hydraulic cylinder and piston combination and the manually actuated actuating means comprises an adjustable screw means integral with the hydraulic cylinder and piston combination.

9. A workpiece securing system according to claim 8 in which the hydraulic cylinder and piston combination is in the form of a cartridge which can be inserted into and removed from a moving clamp.

10. A workpiece securing system according to any of claims 1 to 9 in which the moving jaw clamp has indexing means to the surface ofthe work table, such that the clamp is indexed to a number of discrete locations on the work table in the direction of movement of the jaw.

11. A workpiece securing system according to claim 10 in which the movement of the jaw resulting from actuation of the mechanically powered actuation is less than the distance between the indexed locations.

12. A moving jaw clamp for use in a workpiece securing system according to any of the preceding claims.

13. A workpiece securing system substantially as described herein with specific reference to the drawings.