GB2076321A - Movable work tables - Google Patents

Abstract

A work table comprises a stationary base plate 12, an overlying intermediate plate 14 and an upper work plate 16 with pairs of spaced parallel roller bail tracks 18 disposed between confronting faces of the plates. The tracks between one pair of plates are at right angles to those between the other pair of plates to enable the upper work plate to be movable in the perpendicular directions. Preferably, the roller tracks are provided as rectangular grooves in the facing surfaces of the plates and hardened rods are positioned in the lower corners to form the bearing surfaces on which the roller balls roll. The table is particularly useful in wire bonding machines used for making connections between integrated circuit chips and the grids on which they are mounted.

Description

SPECIFICATION Movable work tables This invention relates to movable work tables capable of movement in two transverse directions parallel to the plane of the table. Such tables are particularly but not exclusively useful in wire bonding machines used for making connections between integrated circuit chips and the grids on which they are mounted.

In the machines having such tables it is usually necessary for the table to be capable of being moved by reproducible and accurate amounts in either or both of the two transverse directions, hereinafter called the X and Y directions for convenience. Also, it is usually important that any movement in a direction transverse to the plane of the table, i.e.

the vertical direction during movements in the X and/or Y directions be zero or as near zero as possible. In the case of wire bonding machines, particularly those which affect bonding ultrasonically, these requirements are very critical.

Therefore there is a requirement for tables which can move very smoothly and accurately under the effect of low forces in the X and Y directions without any significant movement transverse to the plane containing the X and Y directions, and it is an object of this invention to provide such a table.

According to the invention there is provided a work table capable of movement in either or both horizontal directions X and Y at right angles to one another, comprising a stationary base plate having a pair of spaced parallel roller ball tracks at its upper surface, an overlying intermediate plate having a corresponding pair of roller ball tracks at its underside and balls positioned in the tracks between the two plates so that the intermediate plate rests on and is constrained to move relative the base plate in a direction parallel to the tracks, a further pair of spaced parallel roller ball tracks at the upper surface of the intermediate plate at right angles to the said corresponding pair at its underside, and an upper movable work plate having a corresponding pair of roller ball tracks at its underside and balls positioned in the tracks between the intermediate and upper plates so that the upper work plate rests on and is constrained to move relative the intermediate plate in a direction parallel to those tracks in a direction at right angles to the direction of movement of the intermediate plate relative the stationary base plate.

Such a work table provides the free and smooth movement required to enable small repeatable movements to be made as required in, for example, automated production, particularly for wire bonding machines. Further the table has the advantage that any slight wear which occurs does not require a complicated procedure to eliminate and does not result in backlash or irregular table movement.

Accuracy of table movement requires closely fitting tracks with substantially no looseness or "play" in the assembly. Prior table construction using roller ball tracks locate each pair of tracks on the edges of the plates opposing each other with adjustments to provide the desired fitting tolerance. Such separate adjustments are not required of tables according to the invention since the tracks are self-adjusting because the plates are urged together automatically by their own weight to produce a close fit.

The weights of the intermediate and upper work plates will keep them in position but preferably to prevent accidental displacement and possible damage to the roller balls and their tracks pairs of adjacent plates are resiliently held one against the other. In one simple embodiment of the invention this is achieved by means of spring loaded rollers or wheels carried by one of the pair of adjacent plates which bear against the side of the plate opposite from that adjacent to the other pair of adjacent plates.

The roller ball tracks can be provided in conventional fashion. For example, V-shaped grooves can be provided in the surface of the plates or in track member fitted to those plates and the balls can then roll in and be guided by these grooves. Preferably, however, the tracks are formed by rectangular-shaped recesses or grooves which can be machined accurately and relatively cheaply in the plate and then a pair of spaced hardened rods are laid in the lower corners of these grooves to form the bearing surface on which the balls roll. Such an arrangement is known and provides a simple yet excellent bearing surface.

The weight of the various plates will be relatively consistent throughout the life of the table and so any slight distortion of the bearing surface of these hardened rods will be largely consistent with time.

In the case where grooves are machined in the plates it is preferred that the two parallel grooves in a surface of the plate be machined simultaneously using a tool having two cutting positions spaced apart by the desired amount since this way one can ensure that the two grooves are accurately parallel to one another.

The intermediate table can be formed in a single piece with tracks at its upper and lower surfaces. This is not essential, however, and instead could be formed of two plates joined together one having tracks for cooperation with the base plate and the other having tracks for cooperation with the upper work plate and such an arrangement may have advantages in aligning the two pairs of tracks at right angles to one another.

The upper work table will normally be moved by drive means so that the position of the table in the X and Y axes can be remotely controlled. Thus one drive such as a screwthread drive rotatable by means of an electric stepping motor can be provided between the base plate and the intermediate plate and another provided between the intermediate plate and the upper work plate.

An example of a table according to the invention will now be illustrated with reference to the accompanying drawings, in which: Figure 1 is a plan view of the table; Figure 2 is a side view of the table; Figure 3 is an end view of the table; Figure 4 is a view of the table from underneath; Figure 5 is an enlarged sectional detail across one of the tracks; and Figure 6 is an enlarged sectional detail along one of the tracks.

The table 10 shown in the drawings includes a base plate 12, an intermediate plate 14 and an upper work plate 16 to which can be attached a workpiece, not shown, on which various mechanical operations can be conducted. As best shown in Fig. 1 the base plate 12 is stationary, the intermediate plate is constrained to move in one direction parallel to itself in a direction referred to hereinafter as the X-direction, and the upper plate 16 is constrained to move in a direction parallel to itself in a direction relative to the intermediate plate which is at right angles to the X-direction and is hereinafter referred to as the Y-direction. Therefore relatively to the base plate 12, the upper plate 16 can be moved in the X and Y directions.

Between the base plate 12 and the intermediate plate 14 are a pair of spaced parallel roller tracks 18 and between the intermediate plate 14 and the upper plate 16 are a further pair of spaced parallel roller tracks 18, these latter pair of tracks are however oriented at right angles to the former pair of tracks.

Each roller track is identical and so only one will be described in detail with reference to Figs. 5 and 6. A shallow flat bottomed rectangular groove 20 is formed in each respective plate and then a pair of hardened metal rods 22 are laid in each groove at each corner.

Roller balls 24 are then positioned to roll on the rods 22, the balls being spaced apart by a spacer 26. As best seen in Fig. 5 the balls make point contact with the four rods 22 and roll easily so allowing adjacent tables to move very easily relative one another. Also this type of track 18 has the advantage that, provided the grooves 20 are accurately dimensioned and the rods of consistent diameters, the vertical spacing between the tables will remain constant during relative movements of the tables. Further because the tracks are positioned in facing surfaces of adjacent plates if any wear of the rods does occur, particularly during initial running in", this wear is accommodated by a slight alteration of the vertical spacing of the plates and the tracks do not need separate complicated adjustments to maintain accuracy.

Because the plates bear down on one another directly through the tracks 18 no separate retaining means are necessary be tween each plate. It is preferred however to urge the adjacent plates resiliently against one another so as to avoid accidental displacement of one relative the other. Therefore as best shown in Figs. 2 and 4, a slot 30 is provided through the base plate 12 and a block 32 extends down through this from the interme diate plate. Attached to this block is a spring 34 and rollers or wheels 36 are journalled in the ends of this spring and are urged by the spring against the underside of the base plate 12.In a similar fashion blocks 40 extend up from opposite edges of the intermediate plate 14 and a spring 42 is attached to the top of this block and rollers or wheels 44 are jour nalled in the ends of the spring and are urged by the spring against the upper surface of the upper plate.

Attached to the intermediate plate 14 is a nut assembly 50 having an internal screw thread in which a screw threaded rod 52 works. This rod 52 is rotated by means of a motor 54 mounted on the base plate. In this way rotation of the rod by the motor will move the intermediate plate 14 relative the base plate 12 as the assembly 50 threads along the rod. This will move the intermediate plate and also the upper plate in the Y direc tion. Provided the extent of rotation of the motor can be controlled, e.g. by using a stepping motor, workpieces on the upper plate 16 can be moved very accurately in the X direction.

In a similar manner a nut assembly 56 is provided on the upper plate 16 and a rod 58 works in this and is rotated by a motor 60 mounted on the intermediate plate 14. Then rotation of this motor 60 will move the upper plate and any workpiece mounted on it in the Y direction.

As can be seen the table 10 according to the invention can be made relatively simple, e.g. each parallel pair of grooves 20 in a face of a plate can be machined simultaneously so as to ensure that they are accurately parallel, and thereafter complicated adjustments are either not required either initially or during use to align or keep the tracks aligned and provide accurate movements in the X and Y directions without significant movement of a workpiece in the plate 16 in the vertical direction as that plate is moved in the X and/or Y directions.

Claims (11)

1. A work table capable of movement in either or both directions X and Y at right angles to one another, comprising a stationary base plate having a pair of spaced parallel roller ball tracks at its upper surface, an overlying intermediate plate having a corresponding pair of roller ball tracks at its underside and balls positioned in the tracks between the two plates so that the intermediate plate rests on and is constrained to move relative the base plate in a direction parallel to the tracks, a further pair of spaced parallel roller ball tracks at the upper surface of the intermediate plate at right angles to the said corresponding pair at its underside and an upper movable work plate having a corresponding pair of roller ball tracks at its underside, and balls positioned in the tracks between the intermediate and upper plates so that the upper work plate rests on and is constrained to move relative the intermediate plate in a direction parallel to those tracks in a direction at right angles to the direction of movement of the intermediate plate relative the stationary base plate.

2. A table as claimed in Claim 1 in which pairs of adjacent plates are resiliently held one against the other.

3. A table as claimed in Claim 2 in which pairs of adjacent plates are resiliently held one against the other by spring-loaded rollers or wheels carried by one of the pair of adjacent plates which rollers or wheels bear against the surface of the plate opposite from that adjacent to the other of the pair of adjacent plates.

4. A table as claimed in any preceding claim in which the tracks are formed by rectangular shaped recesses or grooves and a pair of spaced hardened rods are laid in the lower corners of these grooves to form the bearing surfaces on which the balls roll.

5. A table as claimed in any preceding claim in which the tracks are provided by recesses or grooves machined in the surfaces of the plates.

6. A table as claimed in Claim 5 in which pairs of grooves in the surface of the plate have been machined simultaneously using a tool having two cutting portions spaced apart by an amount equal to the desired spacing of the two grooves.

7. A table as claimed in any preceding claim in which the intermediate table comprises a single piece of material with tracks in its upper and lower surfaces.

8. A table as claimed in any of claims 1 to 6 6 in which the intermediate table comprises two plates each having one pair of tracks and joined to one another so that the pairs of tracks are aligned at right angles to one another.

9. A table as claimed in any preceding claim in which drive means are provided to move the upper work plate in the X and Y directions relative to the stationary base plate.

10. A table as claimed in Claim 9 in which the drive means include for each adjacent pair of plates an electric stepping motor attached to one of the pair driving a screwthreaded rod which works in a stationary nut attached to the other of the pair.

11. A work table capable of movement in either or both directions X and Y at right angles to one another, substantially as herein described with reference to the accompanying drawings.