"Machine tool with thermal deformation compensation of measuring means"

[0001] The subject of the present invention is a machine tool, in particular a machine tool of large dimensions, having a device for detecting and compensating the thermal deformations of the measuring means of the machine .

[0002] The need is very much felt to perform high-precision mechanical machining operations on medium and large size mechanical pieces, in work environments not controlled in terms of temperature and humidity such as, for example, large plants located in cold or humid regions, generally where temperatures fall well below 15°C and with large heat fluctuations between day and night.

[0003] In such work environments, it often occurs that, even during machining operations, the piece to be worked and the support on which it is mounted, separate from the machine tool, are cold, as is the surrounding environment, while the parts of the machine tend to heat up .

[0004] As is well known, this not only determines a deformation of the mandrel or the boring bar of the machine tool, such as to make it necessary to use compensation systems, but also a deformation of the measuring means of the machine, e.g., optical lines or linear encoders, introducing a further cause of imprecision of the machining operations.

[0005] The object of the present invention is to make a machine tool, in particular a machine tool of large dimensions, able to solve the aforementioned problem.

[0006] Such object is achieved by a machine tool made according to the claim 1 .

[0007] The characteristics and the advantages of the machine tool according to the present invention are made evident by the description provided below, given by way of example and in a non-limitative way, in agreement with the attached illustrations, wherein:

[0008] - figure 1 shows a plan diagram of a machine tool according to the present invention, in agreement with one embodiment;

[0009] - figures 2 and 3 show enlarged views of the boxes II and III in the figure 1 ;

[0010] - figure 4 represents a front view of the machine tool- in figure 1 ;

[0011] - figure 5 shows an enlarged view of the box V in figure 4;

[0012] - figure 6 represents a plan view of a machine tool according to the present invention, in agreement with a further embodiment; [0013] - figures 7, 8 and 9 show enlarged views of the boxes VII, VII and IX respectively in figure 6; and

[0014] - figure 10 represents a plan diagram of a machining system according to the present invention.

[0015] With reference to the attached illustrations, reference numeral 1 globally denotes a machine tool, e.g., a milling-boring machine of large dimensions, comprising a bench 2 having a mainextension along a main axis X.

[0016] The bench 2 is secured and rests on foundations F and the supporting surface determines a horizontal T floor plane.

[0017] The machine 1 also comprises an upright base 4, which surmounts the bench 2 and is supported by this, translatable in a controllable way along the main axis X. For example, the machine 1 comprises control means of the translation of the upright base, operatively connected with a relative motorisation, to control the controlled translation of the upright base 4.

[0018] The machine 1 also comprises an upright 6, fastened on the upright base 4 and supported by this, having a main extension along a vertical axis Y, at right angles to the T floor plane. The upright 6 preferably has a boxed structure and is delimited by an annular side wall which extends along said vertical axis Y. [0019] The machine 1 also comprises a carriage 8, supported by the upright 6, engaged with the side wall of this, translatable in a controllable way along the vertical axis Y. For example, the machine 1 comprises control means of the translation of the carriage, operatively connected with a relative motorisation, to control the controlled translation of the carriage 8.

[0020] The machine 1 also comprises a mandrel-holder 10, supported by the carriage 8, and a mandrel 12 supported by the mandrel-holder 10, rotatable around a work axis W, at right angles to the vertical axis Y and to the main axis X, to carry out the machining operations; preferably, the mandrel-holder 10 is translatable in the direction of said work axis W, in a controllable way. For example, the machine 1 comprises conrol means of the translation of the mandrel-holder, operatively connected with a relative motorisation, to control the controlled translation of the mandrel-holder 10.

[0021] The machine 1 has at least one position sensor suitable for detecting the position, with respect to a main reference system, of a translatable component of the machine tool 1.

[0022] For example, the machine 1 comprises a position sensor of the upright base 4, suitable for detecting the position of the upright base 4 along the main axis X. Said position sensor, e.g., a linear encoder, comprises an optical line 20, fixed to the bench 2, e.g., on the upper surface of this, positioned along the main extension axis X of said bench.

[0023] The optical line 20. is fixed to the bench 2 in a reference point R; the reference point R realises the origin of the main reference system.

[0024] For example, the reference point R is close to the extremity of the bench 2.

[0025] According to an embodiment variation, the optical line comprises a measuring tape and a case; the case is fixed to the bench. Along the line, the case is split into sections, separated by elastic elements, to accommodate the expansions. Preferably, each section is fixed to the bench.

[0026] The machine 1 also comprises ^' means for detecting the temperature of the optical line 20 suitable for detecting the temperature of the optical line in at least one position along the main axis X and generating respective temperature signals.

[0027] For example, the means for detecting the temperature of the optical line comprise a first temperature sensor Tl, suitable for detecting the temperature of the optical line in a position in the proximity of the reference point R of the optical line 20, a second temperature sensor T2, suitable for detecting the temperature of the optical line in a position distant from the reference point R along the main axis X, and at least one further temperature sensor Tn, suitable for detecting the temperature of the optical line in a position further distant from the reference point R along the main axis X.

[0028] Preferably, said temperature sensors are in contact with the optical line.

[0029] The machine tool 1 also comprises management means 30 operatively connected to the means for detecting the temperature of the optical line and to the control means of the translation of the upright base, suitable for processing the temperature signals coming from said means for detecting the temperature of the optical line and the signals of said control means of the translation of the upright base to determine a correction signal for the translation control means of the upright base according to at least onetemperature of the optical line and taking into account the linear heat expansion coefficient of the optical line.

[0030] For example, the management means are electronic control, devices, e.g., comprising a PLC, a power board or a microprocessor.

[0031] According to a preferred embodiment, furthermore, the machine 1 comprises means for detecting the movement of the reference point R of the optical line, suitable for generating a reference movement signal.

[0032] For example, said means of detection of the movement of the reference point comprise a feeler 40 in contact with the reference point R of the optical line and supported by a fixed locator thermically separated from the bench, e.g., integral with the foundations F on which the machine tool rests.

[0033] For example, according to an embodiment, the feeler 40 is positioned at the extremity of the bench 2 corresponding to the reference point R of the optical line .

[0034] Preferably, said means of detection of the movement of the reference point comprise a column 42, fixed to the foundations F.

[0035] Preferably, furthermore, the means of detection of the movement of the reference point comprise a bar 44 made of substantially indeformable material, e.g., INVAR (with a linear heat expansion coefficient of 1*10-6 1/°C) , fixed on one side of the optical line in correspondence to the reference point and engaged with the feeler 40 on the other side.

[0036] The means of detection of the movement of the reference point are operatively connected to the management means 30 in order to determine a correction signal for the control means of the translation of the upright base according to at least one temperature read along the optical line and according to the signal of movement of the reference point R.

[0037] According to a further embodiment (figure 6) , the reference point R which realises the origin of the main reference system, wherein the optical line is fixed to the bench, is in an intermediate position along the main axis X.

[0038] A machining system 100 comprises the above-described machine tool 1, a piece-holder table 102, positioned opposite the machine, and a piece P to be machined, supported by the piece-holder table (figure 10) .

[0039] For the piece P to be machined or for the table 102, a piece/table V axis is generally identifiable, incident with the main axis X of the bench 2, e.g., at right angles to this.

[0040] In a preferred embodiment, the reference point R which realises the origin of the main reference system, wherein the optical line is preferably fixed to the bench, is at the intersection between the main axis X of the bench 2 and the piece/table V axis.

[0041] According to an even further embodiment (for the sake of convenience always shown in figure 6) , the optical line 20 is fixed on a front face of the bench 2 and the position of the upright base 4 is detected by means of the appendix 50 integral with the upright base and detectable by the optical line.

[0042] For greater clarity, the description has been made above with reference to the translation of the upright base with respect to the bench, along the main axis X.

[0043] According to further embodiment variations, the inventive idea can be generalised by the translation of the carriage with respect to the upright, along the vertical axis Y, or by the translation of the mandrel- holder with respect to the carriage, along the work axis W.

[0044] According to embodiment variations, the above- expressed inventive idea can be applied to horizontal milling-boring machines, vertical mobile gantry milling machines, vertical milling machines with moving tables, turning and milling centres, rotary slot milling machines, roto-translating tables, horizontal machining centres, vertical machining centres, vertical boring machines, boring machines for deep holes, and transfer machines. In particular, it is particularly applicable to large-dimension machine tools, i.e., machine tools for removing shavings, wherein the horizontal dimensions are much greater than those of the single workstation; e.g., for large-dimension horizontal milling-boring machines, the minimum length of the bench is, for example, 4000 mm.

[0045] Innovatively, the machine tool according to the present invention permits an increase in precision of machining operations, including in a work environment which is not controlled in terms of temperature or humidity .

[0046] In particular, advantageously, the machine tool makes it possible to offsetthe elongation of the measuring parts of the machine itself, by cancelling to a large extent the harmful effect of heat deformations.

[0047] In order to satisfy contingent requirements, a technician in the sector could of course make changes to the above-described machine tool, all contained within the scope of protection as defined by the following claims.