GB2061141A - Machine tool - Google Patents

Abstract

An electro-errosion machine tool (10) is provided with a drive means which enables reciprocation of a workpiece (28) in a direction normal to the direction of feed of an electrode (26). A motor (40) is attached to the saddle (14) and rotates a follower (42) which at all times engages a plate (18). The plate (18) is positioned at an angle to the plane of rotation of the follower (42) and thus forces the follower (42) and therefore, saddle (14) to move in a direction parallel with its axis of rotation. A spring (44) returns the saddle and follower to their original positions. <IMAGE>

Description

SPECIFICATION Machine tool This invention relates to a machine tool.

More specifically, the invention relates to a machine tool provided with drive means, to enable relative reciprocatory movement between a forming tool and a workpiece, so as to effect machining of a slot in the workpiece.

The invention seeks to provide a machine tool which has means which interalia, provides the ability to vary the magnitude of the relative reciprocatory movement.

According to the present invention there is provided a machine tool comprising a tool holder, a bed, a saddle slidably supported by said bed and means for achieving linear, reciprocatory movement between the tool holder and saddle, in a direction normal to feed of a tool held by the tool holder into a workpiece supported by said saddle, during operation of the machine tool, said means including a member and a member follower, connected between bed and saddle and adapted for relative rotation with respect to each other, the member having a face which is engaged by the member follower and so shaped and positioned that, on occurrence of a half revolution of said relative rotation, the follower is displaced linearly in one direction and displaces the saddle in similar manner and, on occurrence of a further half revolution of said relative rotation, enables return of said follower and therefore, the saddle on a reciprocal path and means for bringing about said return.

The member may comprise a flat surface, positioned at an angle of less than 900 to a plane normal to the axis of said relative rotation and engaged by said member follower in abutting relationship, such that on a half revolution of said relative rotation taking place, the member follower and therefore, the saddle, is displaced in one direction a distance equal to the required length of a slot being produced.

Alternatively, the member may comprise a toroidal groove, in which said member follower engages via an end thereof, wherein the toroidal groove flies at an angle of less than 900 to a plane normal to the axis of said relative rotation so that, on occurrence of a half revolution of said relative rotation, the mem berfollower and therefore, the saddle are displaced a distance equal to the required length of a slot being produced.

Preferably the member follower is rotatable.

Preferably the member is pivotally supported on the bed, so as to enable angular adjustment of its follower engaging surface, with respect to the plane of relative rotation so as to further enable variation in the magnitude of displacement of the member follower and saddle.

Means may be provided for pivoting said member, comprising an articulated rod assembly, one end of which is pivotally connected to said member and the other end of which is urged against a movable sine bar, such that on movement of said sine bar in a direction normal to the length of the linkage assembly, said linkage assembly moves axially of itself and pivots said member, so as to change the magnitude of displacement of said saddle.

Preferably the sine bar is moved in conjunction with the tool holder.

Resilient means are provided, to urge the rod assembly against the sine bar.

The means for bringing about return of said saddle may comprise resilient means arranged between saddle and bed.

Alternatively the means for bringing about return of the saddle may comprise a hydraulically or mechanically powered mechanism.

The member may comprise a cam rotatably mounted on said bed and positioned so as to be engaged via its periphery, with the memberfollow- er, said periphery being so shaped that on rotation of the cam, the member follower and therefore, the saddle, is displaced in one direction and, on continued rotation of the cam, is enabled to return.

Preferably the cam periphery is so shaped as to cause the magnitude of displacement of the saddle to change for each displacement thereof in one direction.

The invention will now be described, by way of example and with reference to the accompanying drawings in which: Figure 1 is a side view of a machine tool in accordance with an aspect of the invention, Figure 2 is a view in the direction of arrow 2, Figure 3 is a part view of a further embodiment of the machine tool of the invention, In Figure 1 in the present example, an electro discharge machine tool is indicated by the numeral 10. Machine tool 10 includes a bed 12 which is fixed to ground and, a saddle 14 which is slidable on bed 12, to left and right as viewed in the drawing.

Bed 12 also carries an articulated rod 16 in sliding relationship therewith and a member 18 which is pivotally mounted about axis 17, to one end of bed 12. Rod 16 and member 18 are connected at hinge point 20 so that, on movement of rod 16 to left or right, the angular relationship between bed 12 and member 18 is altered.

Avertical column 22 is integral with bed 12, and supports a carriage in sliding relationship. The carriage 24 carries an electrode 26. Sliding of carriage 24 in a vertical reciprocatory manner, moves electrode 26 towards and away from a workpiece 27.

Sliding of carriage 24 is brought about by e.g.

drive via lead screw 25, from a stepping motor (not shown) but can be by any conventional drive means.

A sine bar attachment 28, is located at the foot of carriage 24 and its working face 30 is engaged by the free end of articulated rod 16. The engagement is assured by virture of a coil spring 32 which is positioned between a shoulder 34 on bed 12 and a collar 36 on rod 16, thus urging rod 16 against face 30.

Referring now to the right hand end of the machine tool, as viewed in Figure 1. A stepping motor 40 is affixed to the underside of saddle 14.

Stepping motor 40 carries and, in operation rotates a follower 42, the free end of which at all times engages the adjacent face of member 18. Moreover, the axis of rotation is aligned with pivot 17.

In operation, when follower 42 rotates, its engagement with the face of member 18 results in the applying of a force in a direction axially of the follower. The follower is thus moved to the right as viewed in the drawing, along with stepping motor 40 and saddle 14. One half rotation of follower 42 will move saddle 14 a distance 'A' the magnitude of which, is determined by the angular relationship between the engaging face of member 18 and the plane of rotation of follower40 and, the diameter of the circle described byfollower40, e.g. if the member face is positioned at an angle of 300 to the vertical and, that point on the follower which contacts member 18 describes a circle of 2 units diameter, the magnitude of distance 'A' would be 1 unit.

Member 18 does not act on follower 40, to return it to its original position during the second half rotation. Therefore a coil spring 44 is provided between a shoulder 46 on saddle 14 and a shoulder 48 on bed 12. Re-expansion of spring 44 urges saddle 14 to the left as viewed in the drawing and ensures that follower 40 maintains contact with the engaging face of member 18.

Reciprocation of saddle 40 moves workpiece 28 in similar manner, relative to electrode 26. It follows that, on passing an electric current across electrode and workpiece and introducing a flow of suitable dielectrictherebetween during the reciprocatory movement, a slot 50 will be formed in workpiece 27, the length of the slot being equal to distance 'A' plus the electrnde thickness. The form of slot is shown in Figure 2.

The electrode-26 must be continually moved downwards; towards workpiece 27, in order to bring about further metal removal. Therefore sine bar 28 will be moved by virtue of its connection thereto, via carriage 24. Such downward displacement of sine bar 28 will-enable spring 32 to urge rod 16 to the left as viewed in the drawing, thus pivoting member 18 about axis 17 and, changing the angular relationship between the engaging face of member 18 and the plane of rotation of follower 42.

The angularchange results in the present example, in the shortening of distance A over which saddle 14 and reciprocates as the changing of angular relationship continues, these results, the production of a slot 50 which is tapered, being wider at the top, than at the bottom.

It will be apparentfrom theforegoing description, that the reciprocatory pattern of profile may be varied, by varying the engaging face of the sine bar.

It follows that, a slot 50 may be produced having sides which are paratlel or curved or tapered, or any combination of those shapes. The only limitation is, that in no position within the slot, can dimension 'A' exceed its magnitude at the plane of entry of electrode 26 into workpiece 27.

In a further embodiment of the present invention, member 18 and follower 42 are modified as shown in Figure 3. Member 18 has a toroidal groove 52 formed on its face adjacent the follower 42 and the free end of follower 42 has a spherical form 54 which fits in close sliding engagement in groove 52.

When follower 42 is rotated, the motor 40 arid saddle 14 are first pushed to the right as has been described hereinbefore. On the second half of a complete rotation however, the motor 40 and saddle 14 are pulled to the left, by interaction between the wall of groove 52 and the spherical portion of follower 42. However, when a member 18 lies at an acute angle to the plane of rotation of foliower 42, the end of follower 42 will be forced to follow an elliptical course. Follower 42 must therefore be articulated at Point 43. In this example, spring 44 may be dispensed with.

Where it is required to produce a slot which has parallel sides, which are also normal to the direction of reciprocation of the workpiece 28, sine bar 28, spring 32 and rod 16 may be dispensed with.

Member 18 is locked by any suitable means into a position which provides the desired angular relation Ships with the plane of rotation of follower 42 and, motor 40 actuated to rotate the follower.

Claims (11)

1. A machine tool comprising a tool holder, a bed, a saddle slidably supported on said bed and means for achieving relative linear, reciprocatory movement between the tool holder and saddle, in a direction normal to the direction of feed of the tool holder into a workpiece during operation of the machine tool, said means including a member and a member follower connected between bed and saddle and adapted for relative rotation, the member having a face which is engaged bythe member follower, which face is so shaped and positioned that, on occurrence of a portion of a revolution of said relative rotation, the follower is displaced linearly in one direction and displaces the saddle in similar manner and an occurrence of a further portion of said revolution, enables return of said follower and therefore said saddle, on a reciprocal path and means for bringing about said return.

2. A machine tool as claimed in claim 1 wherein said member comprises a flat s6rtacepositioned at an angle of less than 90Q to a plane normal to the axis of said relative rotation and engaged by said member follower in abutting relationships, such that on a half revolution of said relative rotation taking place the follower and therefore the saddle, is displaced in one direction, a distance equal to the required length of a slot being produced.

3. A machine tool as claimed in claim 1 wherein said member comprises a toroidal groove, in which said member follower engages via an end thereof, wherein the toroidal groove lies at an angle of less than 900 to a plane normal to the axis of said relative rotation so that on occurrence of a half revolution of said relative rotation, the follower and therefore, the saddle, is displaced a distance equal to the required length of a slot being produced.

4. A machine tool as claimed in any previous claim wherein the member follower is rotatable.

5. A machine tool as claimed in any previous claim, wherein said member is pivotally supported on said bed, so as to enable angular adjustment of its follower engaging surface with respect to the plane of relative rotation and thereby vary the magnitude of displacement of follower and saddle.

6. A machine tool as claimed in claim 5 including member pivoting means, comprising an articulated rod assembly, one end of which is pivotally connected to said member and the other end of which is urged against a movable sine bar such that on movement of said sine bar, in a direction normal to the length of the linkage assembly, said linkage assembly moves axially of itself and pivots said member, so as to change the magnitude of movement of the saddle.

7. A machine tool as claimed in claim 6 wherein said sine bar is movable in conjunction with the tool holder.

8. A machine tool as claimed in 7 wherein resilient means is provided to urge the rod assembly against said sine bar.

9. A machine tool as claimed in any previous claim wherein said means for bringing about said relative, reciprocatory movement between saddle and bed includes resilient means adapted and arranged so as to act against the first part of said relative reciprocatory movement brought about by action of said member follower as said member and, on completion of said first part of the reciprocatory movement, bring about relative movement in the opposite direction thereto.

10. A machine tool as claimed in any previous claim, wherein the machine tool is an electro discharge machine tool.

11. A machine tool substantially as described in this specification, with reference to the drawings.