"Device for detecting thermal deformations of a spindle of a machine-tool" DESCRIPTION

[0001] The object of the present invention is a device for detecting the deformations of a spindle of a machine-tool. [0002] In the field of machine tools, especially of large dimensions, the need of manufacturing a mechanical part with increasingly smaller processing tolerances is strongly felt by the users. Such need affects the manufacturers of such machines, which carry out considerable research and development efforts to offer machines with increasingly better performance. [0003] The extent of the processing tolerances that can be obtained for a mechanical part is strongly affected by the thermal and mechanical deformations undergone by the machine support parts, which support a processing tool in a desired position in space.

[0004] Generally, a machine comprises a main guide and a mobile group consisting of a travelling support, sliding on such guide, a spindle carrier, sliding transversal to the travelling support, a spindle, sliding parallel to the spindle carrier and suitable for rotating around its axis of rotation, and a tool holder, which is connectable to a processing tool, arranged at the front end of the spindle .

[0005] While the main guide, especially for large sized machines, exhibits systems for compensating the deformations so far deemed as reliable, the mobile group at present does not exhibit as much effective systems for remedying the deformations of a thermal nature that characterise such zone.

[0006] Several solutions of devices for detecting the deformations undergone by the support parts of a machine- tool exist . [0007] The object of the present invention is to improve the devices currently known, making them such as to detect the thermal deformations occurred with greater reliability. [0008] Such object is achieved by a detection device obtained according to claim 1. The dependent claims describe embodiment variations.

[0009] The features and advantages of the detection device according to the present invention will appear more clearly from the following description, made by way of an indicative and non-limiting example with reference to the following figures, wherein:

[0010] - figure 1 shows a schematic view of a machine tool comprising a detection device according to the present invention, in an retracted position of the spindle and of the spindle carrier;

[0011] - figure 2 shows a diagram of the machine of figure 1, in an extended position of the spindle; and [0012] - figure 3 shows a diagram of a machine tool according to a variation of embodiment, comprising the detection device according to the present invention.

[0013] With reference to the annexed figures, reference numeral 1 globally denotes a machine tool . [0014] According to a preferred embodiment, machine 1 comprises a fixed guide 2, which extends along a prevailing longitudinal direction, for example vertical, that is, perpendicular to the ground surface the machine rests on.

[0015] Moreover, machine 1 comprises a mobile group, associated to guide 2. The mobile group can be moved at least along said longitudinal direction of guide 2 and comprises a travelling support 4, operatively connected to the guide for shifting along said longitudinal direction, and a spindle carrier-spindle unit, supported by travelling support 4 and integral in shifting therewith.

[0016] The spindle carrier-spindle unit, associated to travelling support 4, comprises a spindle carrier 6, in jargon called "ram", and a spindle 8. [0017] Spindle carrier 6 is supported by travelling support 4 and operatively connected thereto so as to shift

relative to said travelling support along an axial direction, perpendicular to the longitudinal direction along which travelling support 4 can shift relative to guide 2. [0018] In particular, spindle carrier 6 is suitable for shifting between a retracted position and an extended position, suitable for executing a process on a mechanical part, wherein spindle carrier 6 protrudes more at the front from travelling support 4 as compared to the retracted position.

[0019] Spindle carrier 6 exhibits an inner space open at the front through a spindle carrier opening. [0020] Moreover, the spindle carrier-spindle unit comprises a spindle 8, at least partly seated in the spindle carrier space.

[0021] Spindle 8 is supported by spindle carrier 6 so as to rotate about an axis of rotation thereof and so as to shift relative to spindle carrier 6 along said axial direction. [0022] In particular, spindle 8 is suitable for shifting between a retracted position and an extended position, suitable for executing a process on a mechanical part, wherein it protrudes at the front from spindle carrier 6 through said spindle carrier opening more than in said retracted position.

[0023] Spindle 8 comprises a signalling element 10, integral in shifting with the spindle, arranged in the proximity of the front end of said spindle. [0024] In other words, the signalling element is arranged, depending on the minimum structural dimensions that characterise it, close to the tool holder usually connected to the front end of the spindle . [0025] For example, said signalling element 10 is made of a hole or a groove into the spindle or an obstacle wall protruding from the spindle.

[0026] Moreover, the spindle carrier-spindle unit comprises a spindle carrier cover 12, in jargon called "dummy cover" , associable at the front with spindle carrier 6 for covering, at least partly, said spindle carrier opening allowing in any case the shifting of spindle 8. [0027] The spindle carrier cover 12 is removably associable to spindle carrier 6.

[0028] In particular, when the use of spindle 8 is required to execute a mechanical process, cover 12 is associated to the spindle carrier, especially for protecting the interface systems for machine accessories (for example square heads, universal heads, etc.) . When the spindle on the other hand is not used, cover 12 is removed from spindle carrier 6 and a processing accessory is associated to the front thereof, for example a milling

head.

[0029] The spindle carrier-spindle unit comprises detection means, attached to the spindle carrier cover 12, suitable for detecting the position of the signalling element 10 of the spindle for detecting the thermal deformation of said spindle in said retracted position.

[0030] For example, the detection means comprise a laser device suitable for emitting a laser beam for detecting the position of the signalling element 10. [0031] According to an embodiment variation, the detection means comprise a switch suitable for opening or closing when influenced by the signalling element 10. [0032] According to a further variation of embodiment , said detection means comprise a proximeter for detecting the position of the signalling element.

[0033] In the following description, two typical states of the machine shall often be referred to: the "cold" state, which characterises the machine after a more or less long standstill machine period and wherein the machine substantially exhibits same dimensions as the project ones, and the "hot state" which characterises the machine after a warming cycle, usually carried out after the standstill period and before a process, or after the execution of a process, wherein the machine exhibits deformed dimensions as compared to project ones,

especially due to the thermal deformations occurred. [0034] Moreover, it should be noted that the retracted spindle position is defined through said detection means . [0035] In other words, when said detection means detect the presence of the signalling element 10 integral to the spindle, the position the spindle has at the time of said signalling is defined as retracted spindle position. [0036] In yet other words, when the hot spindle is moved to the retracted position, the detection means detect the position of the signalling element 10 of the spindle, advantageously arranged in the proximity of the front end of said spindle.

[0037] Said cover 12 and said detection means, cooperating with the signalling element arranged on the spindle make up a device for detecting and consequently compensating the thermal deformation of the spindle.

[0038] According to a preferred embodiment, said mobile group comprises means for detecting the deformation of cover 12 suitable for detecting the thermal deformation optionally undergone by cover 12.

[0039] For example, said means for detecting the deformation of the cover comprise a thermal probe or a cover bar made of a substantially thermally non- deformable material, for example Invar ^® . [0040] Moreover, the spindle carrier-spindle unit comprises

first measurement means suitable for measuring the axial advancement of spindle 8 between a fixed reference position 14 on spindle carrier 6 and a moving reference 16, moving relative to spindle carrier 6 and integral in shifting to spindle 8.

[0041] According to a preferred embodiment, said measurement means comprise:

[0042] - a first optical rule 18 integral in shifting with spindle carrier 6 and fixed to said spindle carrier in a position of rule for spindle, which makes up said fixed reference position 14 on the spindle carrier, and [0043] - a first rule sensor 20, integral in rotation to spindle 8 and suitable for cooperating with said first optical rule 18 for detecting the axial advancement of the spindle .

[0044] In the standard operation of machine 1, while spindle 8 is shifting, the position taken by the first rule sensor 20 is detected by the optical rule 18, thus providing a measurement of the axial advancement of the spindle relative to the spindle carrier. A feedback control allows axially positioning the spindle according to the needs .

[0045] The mobile group comprises second measurement means suitable for measuring the axial advancement of spindle carrier 6 relative to travelling support 4.

[0046] According to a preferred embodiment, said second measurement means comprise:

[0047] - a second optical rule 22 integral in shifting to travelling support 4 and fixed to said travelling support in a position of rule for spindle carrier 24, and

[0048] - a second rule sensor 26, integral in rotation to spindle carrier 6, suitable for cooperating with said second optical rule 22 for detecting the axial advancement of the spindle carrier relative to the travelling support. A feedback control allows axially positioning the spindle carrier according to the needs . [0049] In the standard operation of machine 1, while spindle carrier 6 is shifting, the position taken by the second rule sensor 26 is detected by the optical rule 22, thus providing a measurement of the axial advancement of spindle carrier 6 relative to travelling support 4. [0050] The retracted spindle carrier position is defined through said second measurement means. When the spindle carrier is fully retracted, the rule indicates the maximum spindle carrier stroke; when the spindle carrier is fully forward the rule indicates "zero" and this also corresponds to the rule zero. Moreover, the mobile group comprises second detection means suitable for detecting the thermal deformation of spindle carrier 6. [0051] According to a preferred embodiment, said second

detection means comprise a bar 28 of a substantially thermally non-deformable material .

[0052] The term "substantially thermally non-deformable" material indicates a material for which the thermal expansion coefficient is much lower than that of the material the spindle carrier is made of, for example lower than one tenth of the latter. For example, bar 28 is made of Invar ^® . [0053] Bar 28 mainly extends in axial direction, between a front end, fixed to the spindle carrier in the proximity of the front end thereof, and a back end.

[0054] When cold, the back end of bar 28 is aligned with the position of the second rule sensor 26 of the means for measuring the spindle carrier advancement . [0055] Moreover, said second detection means comprise a bar sensor 30, integral to spindle carrier 6 and suitable for detecting the axial distance of the back end of bar 28. [0056] In the standard operation, during the processing step, the second detection means continuously detect the hot distance between the back end of bar 28 and the bar sensor 30. Based on such detections, the thermal deformation undergone by the spindle carrier is defined and the compensation thereof can thus be carried out. [0057] In an embodiment, the fixing position of the second rule sensor 26 coincides with the rule position for

spindle 14 .

[0058] In a preferred embodiment, on the other hand, the fixing position of the second rule sensor 26 is axially spaced from said rule position for spindle 14. [0059] Advantageously in such preferred but non-exclusive embodiment, the mobile group comprises further detection means suitable for detecting the thermal deformation of the spindle carrier between the fixing position of the second rule sensor 26 and the rule position for spindle 14 (figure 3) .

[0060] Said further detection means are separate and independent of said second detection means . [0061] Said further detection means comprise a further bar 32 of substantially thermally non-deformable material, for example Invar ^® .

[0062] The further detection means further comprise a bar sensor 34, integral to spindle carrier 6 and suitable for detecting the axial distance of said back end of the further bar 32. [0063] When cold, the back end of the further bar 32 is aligned with the rule position for spindle 14. When hot, on the other hand, spindle carrier 6 has undergone a thermal deformation and the back end of the further bar 32 exhibits an axial distance from the rule position for spindle 14.

[0064] During the usual processing steps:

[0065] - the second detection means detect the back end of the first bar 28 and the fixing position of the second rule sensor 26; [0066] - the further detection means detect the distance between the back end of the further bar 32 and the rule position for spindle 14 thus allowing excellent overall detection of the deformations occurred in the mobile group . [0067] Innovatively, the detection device described above allows detecting the thermal deformation undergone by the spindle in a very effective manner, since the signalling element is arranged in a very close position to the front end of the spindle, close to the connection with the tool holder .

[0068] Advantageously, moreover, the first detection means are seated in the cover, thus remaining protected from chips, dirt, coolant and further pollutants generated during the execution of a process . [0069] According to a further advantageous aspect , the first detection means when the spindle is not used and the spindle carrier is associated to a processing accessory, are removed from the working area, thus remaining protected. [0070] According to an even further advantageous aspect ,

the first detection means are integral in shifting with the spindle carrier, allowing the detection of the spindle deformation without having to retract the spindle carrier, thus decreasing the times of some processes and increasing the reliability of the measurement, actually not changing the position taken by the spindle carrier. [0071] It is clear that a man skilled in the art can make changes and variations to the detection device described above, all falling within the scope of protection defined in the following claims.