GB2233925A - Linear motion system - Google Patents

Abstract

In the system, incorporated in a device such as a punching device, an elongate member 25 is supported at both ends on one or both sides of its line of movement by the mid-points of leaf springs 27, 28, (29 and 30, Fig 1). The leaf springs are clamped at their ends to the ends of corresponding, similar leaf springs 9, 10, (11 and 12 Fig 1) mounted in turn at their mid-points to respective fixed frame members 5 and (6 Fig 1). Rigidity is provided to the system by interconnecting in pairs the clamps (16 to 21) at the ends of the leaf springs either by lateral bars or straps or by pillars 13, 14 and (15 Fig 1) aligned parallel to the direction of movement. A punch 22 is clamped to the member 25 at 23 for vertical adjustment and frame members 5 and 6 are also vertically adjustable. The punch, particularly for punching thin material eg. of the order of 10 microns with a punching clearance of 1 micron, is operated manually by means of a knob (26 Fig 1), the operator's hand resting on frame member 4. For thicker workpieces mechanical advantage means can be incorporated. Other applications include precision instruments and probes. <IMAGE>

Description

LINEAR MOTION SYSTEM This invention relates to linear motion systems in which one component is movable in a reciprocating manner. An example of this, to which the invention is particularly, though not exclusively, applicable, is a punching device in which a punch is moved in line with a hole formed in a die. The punch in such a device, particularly in the type in which the punch is retained vertically within a fixed frame and is operated by manual downward pressure applied to its upper end, typically takes the form of a rod of circular cross-section terminating at its lower, cutting end by a generally transverse cutting face the periphery of which constitutes the cutting edge.

For all precise applications it is necessary for there to be a good fit between the punch and die, with a clearance all round of less than about one tenth of the thickness of the material being punched. Thus to produce accurately-formed discs from material 10 microns thick the clearance between punch and die should be less than 1 micron and the repeatable alignment of punch and die should be within this accuracy also.

For these applications it is therefore necessary not only for it to be possible to set up accurate initial alignment of punch and die, but also for this accuracy not to be affected by the differences in the manner of pressure applied to the device by the operators or by slack present in the mechanism of the device present either initially or developing after repeated use.

It is a relatively straightforward matter to achieve good alignment between punch and die by means of a setting-up operation, but by using conventional supports for the punch it is not possible for this alignment to be maintained. The aim of precise linear axial motion of the punch has been attempted by spring-loading the punch against a plurality of bearing surfaces, or "sliders". It is difficult though to achieve an accuracy in the machining or alignment of the bearing surfaces to the required 1 micron or less; the thickness of lubricating fluid is in any case a few microns and variations in the thickness of such fluids, caused for example by variations in the transverse pressure applied to the punch by the operator, could cause significant malalignment.Furthermore, it is difficult to prevent the ingress of dust particles and the like into the bearings, resulting not only in malalignment but also scratching, and eventually wear, of the surfaces.

This invention is intended to provide a linear motion system having a movable member whose supporting and guide mechanism has no bearing surfaces, offers considerable lateral stability to the reciprocable member and is repeatable to a very high degree of accuracy.

This invention consists of a linear motion system having an elongate member movable linearly within a frame and attached for support towards both of its ends to the mid-points of respective, similar leaf springs both the ends of each leaf spring being held in a clamp to the corresponding ends of a similar, parallel leaf spring fixed at its mid-point to a frame member, the said clamps being interconnectable in pairs to maintain a fixed spatial relationship.

The movable member is thus held towards each end by similar, resilient supports together providing considerable stability in at least one lateral plane. Even greater stability results if the movable member is attached to such supports located symmetrically on both sides of the line of movement whereby a linear motion system is provided having an elongate member movable linearly within a frame and attached for support towards both of its ends and symmetrically on both sides of its line of movement to the midpoints of respective, similar leaf springs both the ends of each leaf spring being held in a clamp to the corresponding ends of a similar, parallel leaf spring fixed at its mid-point to a frame member, the said clamps being interconnectable in pairs to maintain a fixed spatial relationship.

If support is provided on both sides of the line of movement, transverse bars may be used to interconnect pairs of clamps disposed symmetrically across the line of movement, but generally it is preferable for the means interconnecting the clamps to comprise rigid pillars parallel to said elongate member. In either case, the leaf springs would be clamped to the opposite ends of each pillar or bar.

By way of example, one embodiment of the invention will now be described with reference to the drawing, of which Figure 1 is a part-sectional front view of a punching device constructed in accordance with the invention and adapted for the production of small discs of material, and Figure 2 is a section along the line II - II of Figure 1.

The punching device, shown in the drawing in a depressed position, consists of a rigid frame comprising a base 1 and two side walls 2 and 3 interconnected towards their rear by a top plate 4 which provides hand support to an operator as well as extra stiffness to the structure.

The guide mechanism for the punch is supported on two support members 5 and 6 each held on a respective side wall by two screws 7 which pass through vertically-elongated slots 8 in the side walls which provide a degree of vertical adjustment.

Four leaf springs 9, 10, 11 and 12 are clamped at their respective mid-points to the top and bottom of both support members and are retained at their ends to the top and bottom of four pillars 13, 14 and 15 (one not shown) by eight clamps 16, 17, 18, 19, 20 and 21 (two not shown).

The punch 22 consists of a hardened steel rod having a lower end which is machined to the required diameter and profile and is retained by a clamp 23 in a vertical groove 24 machined on the centre line of the front face of a plate 25 which also supports a knob 26 on its upper edge.

Four further leaf springs 27, 28, 29 and 30 are clamped at their mid-points to the extremities of the top and bottom edges of the plate 25 and are held at their respective ends by the eight clamps 16 and 21 etc. to the four pillars 13, 14, 15 etc. alongside the leaf springs 9, 10, 11 and 12.

The arrangement just described thus provide a mechanism by which the punch 22 is constrained to move in a precisely straight line by the downward pressure on the knob 26 by an operator against the resilient action of the eight symmetrically-disposed leaf springs.

In an alternative embodiment, one side of the mechanism is dispensed with, so that the plate 25 is supported on one side only by, for example, four leaf springs 9, 10, 27 and 28 interconnected by two pillars 13 and 14. This embodiment provides a sufficiently accurate linear movement provided that the downward force applied to the plate is not sufficient to cause excessive torsion in the springs.

In further alternative embodiments, one or more pairs of clamps (e.g. 18 and 20 or 19 and 21) are replaced, in order to provide additional rigidity, by a single transverse bar interconnecting the respective pillars but it has to be borne in mind that the use of a single bar instead of separate clamps 19 and 21 may obsure the operator's view of the punching operation.

In another alternative embodiment, the front or rear pair, or both pairs, of pillars are replaced by a pair of horizontal straps.

Thus, for example, the front pillars 14 and 15 may be replaced by an upper strap interconnecting the front ends of the upper springs 9, 27, 29 and 11 and a lower strap interconnecting the front ends of the lower springs 10, 28, 30 and 12.

In all these embodiments, the other aspects of the design can be conventional. Thus, if the purpose of the device is to produce perforations in a sheet of material then the cutting face may be inclined to the transverse plane of the punch, but if the purpose of the device is to generate accurately-shaped flat discs of the material then a cutting face as accurately as possible transverse to the axis of the punch - and hence parallel to the material being punched - is usually aimed for.

For some applications it may be preferable to taper the punch behind the cutting edge to give a clearance in order to reduce friction and wear on the punch and die; this is not always necessary however.

For setting up the device for operation, the punch 22 is firstly placed against the groove 24 and clamped on the plate 25 with the cutting portion extending below the clamp 23, and if necessary the vertical position of the support members 5 and 6 is adjusted. A die 31, of conventional design and of the required diameter, is placed on the base 1 over a central cavity 32 and is fixed in position by adhesive which is allowed to set while the mechanism is in the depressed position, ie with the punch located within the die. It is found that even by this simple means a very accurate and maintainable punch/die alignment is achieved.

In operation, the workpiece, ie the material to be perforated whether to produce a perforated sheet of material or to produce discs of the material, is drawn across the die by the operator who, if he wishes, can monitor the process through a viewer. As already mentioned, the alignment of the mechanism is very insensitive to lateral pressure on the knob 26, but even this is minimised by the provision of the top plate 4 on which the operator can rest his hand while depressing the knob with one finger.Unlike some previous designs, the present invention provides good tactile feedback: the operator is directly responsible for the force applied to the punch, against the resilience of the springs, so that he is constantly aware of any variations in the cutting process due, for example, to the ingress of particles, variations in the workpiece or wear of the punch or die, and he is also provided with good control over the length of stroke of the punch (The depression of the plate 25 has been greatly exaggerated in the drawing for clarity - in practice, this depression does not have to be much greater than the thickness of the workpiece but the actual amount will depend on the technique used by the operator).

If the principles of this invention are applied to larger manual punches, for example for perforating rather thick material, a mechanism providing a mechanical advantage to the operator can be incorporated into the design.

It will be apparent to those skilled in the art that the use of this invention is not confined to punching devices. It is applicable as a mechanism for the accurate guidance or control of any device in which there is a requirement for the movement of one member in a precise straight line and not affected by the shortcomings of a bearing system.

Examples of such devices are certain types of instrumentation or probes, and in these the driving force on the movable member may be electromagnetic, for example, or manual.

Claims (8)

1. A linear motion system having an elongate member movable linearly within a frame and attached for support towards both of its ends to the mid-points of respective, similar leaf springs both the ends of each leaf spring being held in a clamp to the corresponding ends of a similar, parallel leaf spring fixed at its mid-point to a frame member, the said clamps being interconnectable in pairs to maintain a fixed spatial relationship.

2. A linear motion system having an elongate member movable linearly within a frame and attached for support towards both of its ends and symmetrically on both sides of its line of movement to the mid-points of respective, similar leaf springs both the ends of each leaf spring being held in a clamp to the corresponding ends of a similar, parallel leaf spring fixed at its mid-point to a frame member, the said clamps being interconnectable in pairs to maintain a fixed spatial relationship.

3. A linear motion system according to Claim 2 in which at least one pair of Clamps disposed symmetrically across the line of motion is interconnected by a rigid bar.

4. A linear motion system according to any preceding claim in which the clamps retain the ends of the leaf springs in a side-by-sidecon- figuration and the mid-point attachments for the springs of such a pair are located generally beside one another.

5. A linear motion system according to any preceding claim in which the means interconnecting the clamps comprise rigid pillars parallel to said elongate member, the leaf springs being clamped to opposite ends of each pillar.

6. A punching device incorporating a linear motion system according to any preceding claim and in which a punch is mounted on said elongate member and is movable linearly in line With a die mounted on the frame.

7. A manually operable punching device according to Claim 6 in which the frame includes a support bar for an operator's hand and the elongate member includes means close to the line of movement of the punch for locating the operator's operating finger.

8. A manually operable punching device substantially as hereinbefore described with reference to the drawing.