Machine tool with device for driving a spindle mounting slide

Abstract: In a machine tool (1) comprising a spindle mounting slide (4) which is driven by a linear electric motor (10) and which runs in a vertical direction (V) in a slideway (9), the mobile slide (4) comprises two runners (19, 20) designed to engage with corresponding fixed sliding guides (23, 24) integral with the slideway (9), and two roller pads (27, 28) that slide on corresponding longitudinal sliding surfaces (30, 31) which are also integral with the slideway (9).

Description: The present invention relates to a device for driving a spindle mounting slide, according to the preamble of claim 1. (see, for example, EP-A-0 893 196). The invention relates in particular to a device for driving the spindle mounting slide in a machine tool supported by a frame and controlled by linear motors that drive the tool at high speed along one or more axes. In modern automatic machine tools, the tool is usually mounted on a supporting element driven by linear motors along three axes which are perpendicular to each other. Automatic machine tools known in prior art comprise a linear electric motor which provides at least the vertical drive for the spindle mounting slide. The linear electric motor comprises a rotor, also known as primary member or simply "primary" and a stator, also known as secondary member or simply "secondary", the primary being integral with the spindle mounting slide, and the secondary being integral with the vertical slideway in which the slide runs. The vertical slideway has, symmetrically positioned at the bottom of it, two pairs of fixed linear guides, for example of the recirculating ball type, which are permanently engaged with two corresponding longitudinal runners made on the mobile slide. The fixed guides also keep the primary and the secondary at a fixed distance from each other, this distance constituting the air gap of the linear motor. The fixed guides are positioned on the vertical slideway at a suitable axial distance from each other to form on the slideway itself a particularly rigid zone that is capable of easily resisting the backlash transmitted by the spindle to the slide during machining. The longitudinal extension of the slide is greater than the axial distance between the two pairs of fixed guides and the distance between the two pairs of guides is approximately equal to the vertical travel of the mobile slide. Indeed, lengthening the longitudinal extension of the fixed guides would unduly encumber the machine tool, with negative repercussions on the accuracy and performance of the machine. Adding more pairs of fixed guides, although it does not considerably increase the weight of the slideway, nevertheless makes it necessary to lengthen the longitudinal runners in order to make the coupling between runner and guide permanent. If the coupling were not permanent, there would be a serious risk of dangerous collisions with the ends of the runners when they enter the guides on account of the high speed at which the spindle mounting slide moves. For obvious practical purposes, the primary of the linear motor, which is mounted close to the upper part of the mobile slide, occupies a longitudinal portion of the slide itself so that it permanently faces the secondary which is fixed to the vertical slideway. When the spindle mounting slide is driven to its uppermost position, the part of the slide with the primary on it projects with respect to the support offered to it by the fixed sliding guides and, consequently, the considerable magnetic force between the primary and the secondary attracts the primary and the secondary to each other. This tends to bend the slide and to move it out of alignment relative to its fixed support, with negative repercussions on machining precision. The aim of the present invention is to overcome the above mentioned disadvantage by providing a device that is used to drive the spindle mounting slide and that is light, compact and economical to construct. The present invention accordingly provides a machine tool comprising at least one spindle mounting slide extending mainly longitudinally along a defined axis and able to move in a direction parallel to said axis at least between a first retracted end position and a second extended end position relative to a fixed slideway extending in said direction, driven by at least one linear electric motor, a primary member of which is connected to the slide and a secondary member of which is connected to the slideway, said slideway comprising fixed sliding guides which are integral with the slideway itself, extend longitudinally in said direction for a distance shorter than the longitudinal extension of the secondary member and engage with runners that are integral with the slide, a longitudinal portion of the spindle mounting slide comprising at least one portion of the primary member which projects with respect to the fixed sliding guides at at least one of the two end positions of the slide itself, the machine tool being characterised in that the slide comprises sliding contact means that oppose the slideway at least when the portion of the primary member is in the position where it projects with respect to the fixed sliding means and the magnetic force is attracting the primary member and the secondary member of the linear electric motor to each other. The invention will now be described with reference to the accompanying drawings which illustrate a preferred embodiment of it and in which: Figure 1 is a schematic perspective view of a machine tool made in accordance with the present invention; Figure 2 is a schematic perspective detail view of a part of the machine tool shown in Figure 1, and illustrates the part in a first, retracted operating position; Figure 3 is a schematic perspective detail view of the part shown in Figure 2, and illustrates the part in a second, extended operating position. With reference to Figure 1, the numeral 1 denotes in its entirety an automatic machine tool of the numeric control type mounted on a base 2. The machine 1 is equipped with an operating module 3 that can move in three-dimensional space along the three linear axes X, Y and Z of a Cartesian system. The operating module 3 comprises a slide 4 that mounts a spindle 5 which transmits rotational cutting motion to a customary cutting tool that is not illustrated. The slide 4 extends mainly along a longitudinal axis T and can move in a vertical direction V parallel to the aforementioned Y axis between a first retracted end position, illustrated in Figure 2, and a second extended end position, illustrated in Figure 3. The machine 1 illustrated in Figure 1 is also equipped with a customary magazine, which is not illustrated in detail and is schematically labelled 6. This magazine houses a plurality of tools which the operating module 3 can access at any time during a machining cycle to automatically change tool whenever a different tool is required for a different machining operation. As shown in Figures 2 and 3, the lower end 7 of the slide 4 mounts the spindle 5 to which the aforementioned tools (not illustrated) are fitted, and presents a parallelepiped shaped protrusion 8, extending longitudinally and housing the equipment used to drive the spindle 5 and which is of customary type and therefore not illustrated. The slide 4 is supported and guided in its vertical movement by a slideway 9 that is mounted in fixed position relative to the vertical direction V and also extending longitudinally along the direction V itself. The slide 4 is driven by a linear electric motor 10 comprising a primary member or rotor 11 and a secondary member or stator 12. Again with reference to Figures 2 and 3, the primary member or rotor 11 is mounted on and connected to the slide 4 at an upper end 13 of it, opposite the aforementioned lower end. The secondary member or stator 12 extends longitudinally along the full length of the slideway 9 and is integral with the slideway. The primary member 11 and the secondary member 12 are positioned opposite each other and separated by a suitable air gap 14 according to the known operating principle of linear electric motors. At its edges 15, 16, symmetrically opposite each other relative to the axis T, the slide 4 has two thin longitudinal portions 17, 18 constituting two runners 19, 20 each designed to engage with a corresponding pair 21, 22 of fixed sliding guides 23, 24, respectively upper and lower, which are integral with the slideway 9 at two corresponding edges 9a, 9b to form a sliding fit between the slide 4 and the slideway 9. The guides 23, 24 of each pair 21, 22 constitute fixed sliding means denoted in their entirety by the numeral 25. Advantageously, these guides 23, 24 are of the recirculating ball or roller type. With reference to Figures 2 and 3, the two, upper and lower guides 23, 24 of each pair 21, 22 delimit a lower portion 26 of the slideway 9, this portion having a larger cross section than the rest of the slideway so as to confer maximum rigidity on the operating module 3 during machining. With reference to Figures 2 and 3, the upper end 13 of the slide 4 presents two pads 27, 28 positioned symmetrically opposite each other relative to the axis T and together constituting sliding contact means 29 for the slide 4 as it moves relative to the slideway 9. In the preferred embodiment illustrated in the drawings, the pads 27 and 28 are of the type with rollers that run on corresponding longitudinal sliding surfaces 30, 31 which are integral with the slideway 9 and are located symmetrically opposite each other relative to the axis T at corresponding lateral zones 32, 33 of the slideway 9 itself. During operation of the machine 1, the spindle mounting slide 4 moves rapidly in direction V towards and away from the workpiece. As shown in Figure 2, when the slide 4 reaches the upper position, which is retracted relative to the vertically fixed slideway 9, the primary 11 faces the secondary 12 in a configuration in which the upper end 13 of the slide 4 is not supported by the fixed guides 23, 24. As shown in Figure 3, instead, when the slide 4 reaches the extended position relative to the slideway 9, the primary 11 faces the secondary 12 in a zone forming part of the longitudinal portion delimited by the guides 23, 24 and which is therefore especially rigid. In this extended configuration, the pads 27, 28 keep the air gap 14 at a constant value by preventing the primary member 11 and the secondary member 12 from moving closer to each other on account of the strong magnetic force created by the flow of current.

Claims: A machine tool comprising at least one spindle mounting slide (4) extending mainly longitudinally along a defined axis (T) and able to move in a direction (V) parallel to said axis (T) at least between a first retracted end position and a second extended end position relative to a fixed slideway (9) extending in said direction (V), driven by at least one linear electric motor (10) a primary member (11) of which is connected to the slide (4) and a secondary member (12) of which is connected to the slideway (9), said slideway (9) comprising fixed sliding means (25) which are integral with the slideway (9) itself, extend longitudinally in said direction (V) for a distance shorter than the longitudinal extension of the secondary member (12) and engage with runners (19, 20) which are integral with the slide (4), a longitudinal portion of the spindle mounting slide (4) comprising at least one portion of the primary member (11) which projects with respect to the fixed sliding means (25) at at least one of the two end positions of the slide (4) itself, the machine tool being characterised in that the slide comprises sliding contact means (29) that oppose the slideway (9) at least when the portion of the primary member (11) is in the position where it projects with respect to the fixed sliding means (25) and the magnetic force is attracting the primary member (11) and the secondary member (12) of the linear electric motor (10) to each other. The machine tool according to claim 1, characterised in that the fixed sliding means (25) comprise at least two guides (23, 24) located on the slideway (9) on opposite sides of the axis (T). The machine tool according to claim 1, characterised in that the fixed sliding means (25) comprise at least two pairs (21, 22) of guides (23, 24) located on the slideway (9) on opposite sides of the axis (T). The machine tool according to claim 2 or 3, characterised in that the guides (23, 24) are of the recirculating ball type. The machine tool according to claim 2 or 3, characterised in that the guides (23, 24) are of the roller type. The machine tool according to any of the foregoing claims, characterised in that the sliding contact means (29) comprise at least one pad (27, 28) that is integral with the slide (4) and designed to engage with at least one corresponding sliding surface (30, 31) that is integral with the slideway (9). The machine tool according to claim 6, characterised in that the pad (27, 28) is of the roller type.

Inventors: FERRARI MAURIZIO, MASSARI CARLO, FERRARI, MAURIZIO, MASSARI, CARLO
Applicants: JOBS SPA, JOBS S.P.A.
Application year: 2001
Main classification: B23Q5
IPC codes: B23Q5, B23Q1, B23B21