GB2163678A - Moving and positioning machine tool slides - Google Patents

Abstract

Positioning apparatus comprises an elongate fixed bed 2, a carriage (3) moveable along the bed, and support 4 also moveable along the bed. The support is drivingly connected to the carriage by a drive coupling, e.g. screw 8 on carriage 3 and nut 15 on support 4, and drive 9 drives the coupling. First location means 12 are locate the carriage at a plurality of fixed positions along the bed and second location means 16 locate the support 4 at a plurality of fixed positions along the bed. The drive coupling is such that when the carriage 3 is located in a fixed position along the bed operation of the drive 9 causes the support 4 to move along the bed and when the support 4 is located in a fixed position along the bed operation of the drive coupling causes the carriage 3 to move along the bed. <IMAGE>

Description

SPECIFICATION Positioning apparatus The present invention relates to positioning apparatus such as may be used for example, for positioning a work tool or a work piece at a desired location.

The accurate positioning of a work tool is an essential requirement for most types of machine tools. However difficulties may arise if the work-tool needs to be moved over comparatively long distances as accuracy of movement will be lost. Thus, even recirculating ball screws which are frequently used to provide accurate movement of a work tool, are only accurate up to, at best, 10 metres or so.

Such limitations in the accuracy of movement of a work tool is a particular problem in the case of fixed-bed machine tools which may have a bed length of 20 metres over which the work tool may need to be moved for processing large workpieces (e.g. ships propellors, press-components etc) positioned alongside the bed.

Similar considerations apply to apparatus which is intended for use in moving a work piece relative to a stationary work tools.

It is an object of this invention to obviate or mitigate the abovementioned disadvantages.

According to the present invention there is provided positioning apparatus comprising an elongate fixed bed, a carriage moveable along the bed, support means moveable along the bed, the support means being drivingly connected to the carriage by drive coupling means, drive means for driving said drive coupling means, first location means associated with the carriage for locating the carriage at a plurality of fixed positions along the bed, and second location means for locating the support means at a plurality of fixed positions along the bed, said drive coupling means being such that when the carriage is located in a fixed position along the bed operation of the drive mearis causes the support means to move along the bed and when support means is located in a fixed position along the bed operation of the drive coupling means causes the carriage to move along the bed.

The apparatus in accordance with the invention is such that the support means (which may for example support a work tool or a work piece) is moveable in a working range along the carriage when the latter is located in a fixed position, and the carriage is itself moveable (by locating the support means in a fixed position and operating the drive means) to a plurality of positions along the bed. At each such fixed position of the carriage, the support means may be moved over its working range along the carriage. Consequently the support means is operable in a plurality of discrete working ranges along the bed whereby the support means may be located at any position along the bed.Since the drive coupling means is only required to move the support means along the length of the carriage, the drive coupling means may be conventional components known to give the accuracy required over the working range of the support means.

The invention will be further described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a side view of one embodiment of fixed bed machine tool in accordance with the invention; and Fig. 2 is a sectional view along arrows Il-Il of Fig. 1.

The fixed bed machine tool 1 illustrated in the drawings is a mono-bed machine (e.g. a floor-borer) and includes an elongate fixed bed 2, an elongate carriage 3, and a saddle 4 for supporting a work-tool (not shown), the carriage 3 and saddle 4 each being moveable along the bed 2 in the manner to be described.

Bed 2 may, for example, be up to 20 metres long and for ease of manufacture may be constructed in separate sections 2a and 2b.

Carriage 3 is of generally H-shaped crosssection (Fig. 2) but with heads 5a and 5b at its left and right hand ends respectively (as viewed in Fig. 1). Carriage 3 is mounted for linear movement in a slideway 6 which extends within the top of bed 2 and within slideway 6 the carriage 3 is guided by projection 7. The upper edge of carriage 3 is level with the upper surface of bed 2.

A drive screw 8 of a length which is comparatively short composed to the length of bed 2 extends along carriage 3 and, at its left hand end (as viewed in Fig. 1) is journalled in head 5a whereas, at its right hand end, it extends through head 5b and is mounted in a drive unit 9 positioned on the carriage 3 to the right of head 5b. The drive unit is itself comprised of a drive motor 10 and reduction gearing 11 whereby screw 8 is rotated on operation of motor 10.

Additionally associated with carriage 3 is a locating unit 12 with a plunger 13 which is locatable in any one of a plurality of recesses 14 spaced along the floor of slideaway 6.

Locating unit 12 is constructed such that plunger 13 is moveable under spring pressure to engage in a recess 14 and is moveable under hydraulic pressure for release from said recess. With plunger 13 located in a recess 14, the carriage 3 is located in a fixed position along the bed 2.

Saddle 4 is slideable along the top of bed 2 (see Fig. 2) and thus over the carriage 3. Provided on the underside of saddle 3 at the right hand end thereof is a nut 15 through which drive screw 8 extends in engagement therewith. In the illustrated embodiment, the drive screw 8 and nut 15 are a conventional recirculate ball-screw arrangement.

A locating unit 16 is carried by saddle 4 and has a plunger 17 which is locatable in any one of a plurality of recesses 18 provided in spaced relationship along the upper surface of bed 2, Locating unit 16 is constructed such that plunger 17 is moveable under hydraulic pressure to engage in a recess 18 and is moveable under spring pressure for release from said recess. With plunger 17 located in a recess 18, the saddle 2 is located in a fixed position along the bed 2.

Recesses 18 are so positioned in relation to recesses 14 that when plunger 13 is located in a recess 14 to clamp carriage 3 in a fixed position, the plunger 17 will locate in a recess 18 when the saddle 4 has been moved (in the manner to be described) to either of its extreme positions of movement along carriage 3.

Additional hydraulic clamps 19 are provided for securing saddle 4 in a fixed position along the bed 2, and clamps 20 are provided for securing carriage 3 in a fixed position along the bed 2.

Further features of the illustrated machine tool 1 relate to the control system therefor.

The machine tool 1 will be associated with a control system for positioning the carriage 3 and saddle 4 as required. Thus, for example, the positions of the carriage 3 and saddle 4 may be monitored by transducer arrangements (Fig. 2 shows a transducer arrangment 21 for monitoring the position of saddle 4 along bed 2). The control system will be such that carriage 3 may be moved automatically to a position at which its associated plunger 13 can be located in a recess 14. Confirmation that the carriage 3 has been moved to the required position may be provided by micro-switch elements 22 positioned on the side of carriage 3 which are co-operable with micro-switch elements 23 provided at appropriate intervals along the adjacent side of slideway 6.

The operation of the illustrated machine tool 1 will now be described.

In order to effect movement of the saddle 4 relative to the bed 2, plunger 13 is located in a recess 14 and hydraulic clamps 20 applied to clamp carriage 3 in a fixed position. Additionally plunger 17 is disengaged from a recess 18 and hydraulic clamps 19 are in a nonclamping positions. Operation of drive motor 10 to effect rotation of drive screw 8 causes nut 15 to move along the screw 8 and thus saddle 4 moves along bed 2 in a working range determined by the spacing of heads 5a and 5b. It will of course be appreciated that the direction of movement of saddle 4 (left or right as viewed in Fig. 1) depends on the direction of rotation of screw 8.

Provided that a work-piece (not shown) to be machined in positioned within the working range of saddle 4 in a given fixed position of carriage 3, the necessary machining operation may be effected.

If however the workpiece is not within the range of the saddle 4 then the following operations are performed. Firstly saddle 4 is moved as far as possible along carriage 3 towards the workpiece. Secondly, plunger 17 is engaged in the adjacent recess 18, clamps 19 are engaged (whereby saddle 4 is located in a fixed position on bed 2) and plunger 13 is disengaged from recess 14, and hydraulic clamps 20 released.

Due to the engagement of screw 8 with nut 15 and the fixed positioning of saddle 4, operation of drive motor 10 now causes carriage 3 to move along bed 2 under the influence of the control system to a position at which plunger 13 can be located in another recess 14 (this position being confirmed by the micro-switch elements 22 and 23). Once clamps 19 have been disengaged and plunger 17 released from recess 18, the saddle 4 may once again be moved in the manner described above.

It will thus be seen that carriage 3 is locateable at a plurality of positions and, at each such position, the saddle 4 is moveable over its working range so that, in total, saddle 4 (and hence its associated work-tool) may be located at any position along bed 2. Since drive-screw 8 need only be of a length below that at which such screws cease to give sufficient accuracy, it will be appreciated that saddle 4 is accurately moveable over the entire length of bed 2.

It will be appreciated that a number of modifications may be made to the illustrated apparatus. Thus, for example the drive-screw 8 may be non-rotatably mounted on carriage 3 and the drive unit may be mounted on saddle 4 to effect rotation of nut 15.

Alternatively the illustrated recirculating ball screw arrangements may be replaced by the forms of transmission where the advantage afforded by such ball screw (e.g. high efficiency and freedom from backlash) are not required.

Such other forms of transmission could be a conventional screw, or a rack and pinion coupled to an electric of hydraulic motor.

Although the invention has been described specifically with reference. to a mono-bed machine, it will be appreciated that the invention may also be applied to a twin-bed machine such as a gantry type machine. Such a machine would comprise two parallel beds with synchronised drive-units, and a gantry between the beds moveable in the same manner as the saddle 4 described above.

It will also be appreciated that the apparatus of the invention may be constructed so as to move a work-piece relative to a work-tool located in a fixed position along the apparatus.

Claims (7)

1. Positioning apparatus comprising an elongate fixed bed, a carriage moveable along the bed, support means moveable along the bed, the support means being drivingly connected to the carriage by drive coupling means, drive means for driving said drive coupling means, first location means associated with the carriage for locating the carriage at a plurality of fixed positions along the bed, and second location means for locating the support means at a plurality of fixed positions along the bed, said drive coupling means being such that when the carriage is located in a fixed position along the bed operation of the drive means causes the support means to move along the bed and when the support means is located in a fixed position along the bed operation of the drive coupling means causes the carriage to move along the bed.

2. Apparatus as claimed in claim 1 wherein the drive coupling means comprises a nut mounted on the support means and a drive screw which is mounted on the carriage and which is in screw-threaded engage; ment with the nut.

3. Apparatus as claimed in claim 2 wherein the drive coupling means is a recirculating ballscrew.

4. Apparatus as claimed in any one of claims 1 to 3 wherein the carriage is mounted in a slideway extending within the bed.

5. Apparatus as claimed in claim 4 wherein the first location means comprises a plunger mounted on the carriage and selectively locatable in one of a plurality of recesses provided in the slideway.

6. Apparatus as claimed in claim 4 or 5 wherein the second location means comprises a plunger mounted on the support means and selectively locatable in one of a plurality of recesses provided along the bed.

7. Positioning apparatus substantially as hereinbefore described with reference to the accompanying drawings.