Patent Description:
Nowadays the need is increasingly felt, by makers of mechanical components for removing material, to be capable of providing products of increasingly higher quality while at the same time also increasing productivity.

This requires machine tools for which an increase in the overall performance is not obtained at the expense of the quality of the product.

Essential requirements for a machine tool are the capacity to move rapidly along complex trajectories while retaining a high precision in its movements, and the ability to remove material as rapidly as possible without generating excessive vibrations, together with the ability to verify directly, on the machine, the quality of the machined piece, by factoring in the qualities typical of coordinate measuring machines (CMM).

Nowadays makers of machine tools strive to adopt light structures to allow higher accelerations that make it possible to minimize the costs of construction, reduce energy consumption, and maximize productivity; in such context what becomes increasingly important is the interaction between the control systems and the dynamic of the mechanical parts in motion, taking account of the deformations of the structure of the machine tool with the variation, for example, of environmental conditions.

In particular, the accuracy of Cartesian numerically controlled machine tools of large dimensions, i.e. with an excursion of the controlled axes that exceeds five meters, is limited by structural deformations that affect the components of the chassis.

Such machine tools are designed to provide a piece by way of a series of activities that are adapted to define such piece so that its shape and its dimensions reflect those specified by a corresponding technical drawing, and such drawing for each geometric peculiarity defines the tolerances which must be verified by way of suitable measuring activities.

Usually, for mechanical pieces of large dimensions, although verifying the tolerances achieved is necessary, it is not performed owing to the costs that such procedure would require.

In fact, a machine tool is a means of production that, during its life cycle, must be kept in optimal conditions of efficiency if it is to be capable of operating within the limits specified by the maker and so as to provide products that conform to the tolerances specified by the design.

Machine tools in fact suffer degradation of performance over time, owing to the surrounding environmental conditions, thus losing reliability.

For this reason, machine tools must be periodically checked to analyze the state of the machine and to be able to define the interventions necessary to maintain the machine in the operating conditions as originally specified.

Nowadays checking the correct operation of a machine tool is done with special measurement and analysis systems, which are adapted to be installed in the neighborhood of such machine tool, and with systems for checking the product provided, such as coordinate measuring machines (CMM).

<CIT> discloses an alignment system for a machine numerically controlled tool.

The aim of the present invention is to provide a Cartesian numerically controlled machine tool for high-precision machining, which is capable of
overcoming the above mentioned drawbacks of conventional machine tools. In particular, within this aim an object of the invention is to provide a machine tool with which it is possible to determine with precision the displacements of the machining head with respect to the specified operating positions and trajectories.

Another object of the invention is to provide an apparatus in order to determine such displacements.

Another object of the invention is to provide a machine tool that is rapidly adaptable to the vibrational and environmental conditions of operation.

This aim and these and other objects which will become better evident hereinafter are achieved by a Cartesian numerically controlled machine tool for high-precision machining, according to claim <NUM>.

Further characteristics and advantages of the invention will become better apparent from the description of six preferred, but not exclusive, embodiments of the machine tool according to the invention, which are illustrated for the purposes of non-limiting example in the accompanying drawings wherein:.

With reference to the figures, a Cartesian numerically controlled machine tool for high-precision machining according to the invention is generally designated with the reference numeral <NUM>.

as shown schematically for the purposes of example in <FIG>.

The Cartesian machine tool <NUM> comprises, on board, optical means <NUM> for detecting and monitoring the position of at least one reference nodal point for each of one or more of the controlled axes X1, X2, X3 with respect to a reference device <NUM> which is integral with a part of the machine tool <NUM>.

Reference nodal points are therefore established on the various parts of the machine tool <NUM>, for example a reference nodal point A for the footing <NUM>, a reference nodal point B for the first part <NUM> of the machine tool, a reference nodal point C for the second part <NUM>, and a reference nodal point D for the third part <NUM>.

By periodically measuring the movements of the nodal point B with respect to the nodal point A it is possible to determine, for example, the deformations of the first part <NUM> with respect to the footing <NUM>.

Similarly, again for example, by periodically measuring the movements of the nodal point C with respect to the nodal point B it is possible to determine the deformations of the second part <NUM> with respect to the first part <NUM>.

In the first embodiment of the machine tool <NUM> according to the invention, such reference device <NUM> is integral with the footing <NUM> and is associated with the nodal point A.

The nodal points are obviously understood to be regions where the components of the means of detection and monitoring are positioned.

It should be understood that the reference device <NUM> is part of the optical means <NUM> of detection and monitoring.

Such optical means <NUM> comprise, as shown schematically in <FIG>, at least one device <NUM> for detecting the translation of a nodal point of a controlled axis, for example of the nodal point B relating to the first part <NUM> and therefore to the axis X1, along two axes X2 and X3 which are perpendicular to the controlled axis X1.

Such device <NUM> for detecting the translation of a nodal point comprises, for example, an emitter of a laser beam <NUM>, which is adapted to be fixed to a part of the machine, for example to the footing <NUM>, at a first nodal point, for example the nodal point A, and an element for receiving the light signal, for example an optical position sensor <NUM>, known in the sector as a Position Sensitive Device (PSD), which is capable of measuring the position of a point of light emitted by the laser emitter <NUM> with respect to two axes which are mutually perpendicular, and is adapted to be positioned at a second nodal point, for example the nodal point B.

The laser emitter <NUM> is arranged so as to be integral with a first part of the machine tool, for example, as mentioned, the footing <NUM>, in such a way that its laser beam <NUM> is parallel to an axis X1 to detect and monitor for deformations, while the optical position sensor <NUM> is arranged so as to be integral with a second part of the machine, for example integral with the second part <NUM>, which is designed to slide on the first part <NUM> of the machine along the axis X1.

The optical position sensor <NUM> is positioned so that when calibration is complete the point of light produced by the laser beam <NUM> is at the origin of the reference axes X2 and X3 of the optical sensor <NUM>.

In this manner it is possible to detect the relative translations of the laser emitter <NUM> with respect to the optical sensor <NUM> according to the axes X2 and X3, indicated in <FIG> with D2 and D3 respectively.

The optical means <NUM> comprise, as shown schematically in <FIG>, at least one device <NUM> for detecting the rotation of a controlled axis, for example the axis X1, about two axes, X2 and X3, which are perpendicular to such controlled axis, and at a reference nodal point.

Such device <NUM> for detecting the rotation of a controlled axis comprises, for example:.

In this manner it is possible to detect the rotations of the mirror <NUM> about the axes X2 and X3 at the second nodal point B, the mirror <NUM> being integral with the second part <NUM> of the machine, by calculating them from the translations according to the axes X2 and X3 of the reflected point of light, which are detected by the optical sensor <NUM> and indicated in <FIG> with D2 and D3 respectively.

The optical means <NUM> comprise, as an alternative to the device <NUM> for detecting the translation of a nodal point of a controlled axis and to the device <NUM> for detecting the rotation of a controlled axis, a device <NUM> for simultaneously detecting the translation of a nodal point of a controlled axis along two axes that are perpendicular to that same controlled axis, and the rotation of a controlled axis about two axes that are perpendicular to that same controlled axis.

Such device <NUM> for simultaneously detecting translation and rotation of a controlled axis, for example X1, is shown schematically in <FIG>.

Such device <NUM> for simultaneously detecting translation and rotation of a controlled axis, for example the axis X1, comprises, for example:.

As an alternative to two consecutive devices <NUM> for detecting the translation, one for detecting the translation of a first nodal point referred to a first controlled axis X1, relating to a first part of the machine, for example the first part <NUM>, and another for detecting the translation of a second nodal point referred to a second controlled axis X2, relating to a second part of the machine, for example the second part <NUM>, arranged so as to translate along the axis X1 on the first part <NUM>, the optical means <NUM> can comprise a device <NUM> for simultaneously detecting the translation of two nodal points which are referred to corresponding mutually perpendicular controlled axes, for example the axes X1 and X2 in <FIG>, along two axes that are perpendicular to each controlled axis.

Such device <NUM> for simultaneously detecting the translation of two nodal points, for example B and C, which are referred to mutually perpendicular controlled axes, for example the axis X1 and the axis X2, comprises:.

With such device <NUM> for simultaneously detecting the translation of two nodal points referred to two controlled axes, it is possible to detect the translations of the two axes X1 and X2 with a single laser emitter instead of with two laser emitters.

As an alternative to three consecutive devices <NUM> for detecting the translation, a first for detecting the translation of a first nodal point referred to a first controlled axis X1, relating to a first part of the machine, for example the first part <NUM>, a second for detecting the translation of a second nodal point referred to a second controlled axis X2, relating to a second part of the machine, for example the second part <NUM>, and a third for detecting the translation of a third nodal point referred to a third controlled axis X3, relating to a third part of the machine, for example the third part <NUM>, the optical means <NUM> can comprise a device <NUM> for simultaneously detecting the translation of three nodal points, for example the nodal points B, C and D, which are referred to corresponding mutually perpendicular controlled axes, for example the axes X1, X2 and X3 in <FIG>.

Such device <NUM> for simultaneously detecting the translation of three mutually perpendicular controlled axes comprises:.

Such device <NUM> also comprises a <NUM>° reflection element <NUM>, for example a cubic reflector prism, known as a 'corner reflector', designed to be arranged so that it is integral with a machining head <NUM>, and therefore referable to the fourth nodal point D, such machining head <NUM> being able to move with respect to the third part <NUM> of the machine.

With the use of such <NUM>° reflection element <NUM>, use is made of a passive element by way of which it is possible not to use, at the machining head <NUM>, components that carry electric current and which therefore could negatively affect the operation of the machining head <NUM>.

With such device <NUM> for simultaneously detecting the translation of three nodal points each referred to one of three controlled axes, it is possible to detect the translations of three axes X1, X2 and X3 with a single laser emitter instead of with three laser emitters.

For detecting deformations owing to translation of the part of the machine supporting the machining head <NUM>, for example the third part <NUM>, the means <NUM> of detection and monitoring can comprise a device <NUM> for detecting the translation of the controlled axis X3, with respect to which the machining head <NUM> slides, along two axes that are mutually perpendicular X1 and X2.

Such device <NUM>, shown for the purposes of example in <FIG>, comprises a laser emitter <NUM> which is integral with the third part <NUM> of the machine, referable to the third nodal point C, a <NUM>° reflection element <NUM>, referable to the fourth nodal point D, which is integral with the machining head <NUM>, and an optical position sensor <NUM> which is integral with the third part <NUM> of the machine, referable to the third nodal point C, toward which the laser beam is deflected.

In the first embodiment in <FIG>, which is illustrative and non- limiting of the invention, for detecting and monitoring the linear displacements, i.e. the translations, of the nodal points B, C and D referred to the three axes X1, X2 and X3, the means of detection and monitoring <NUM> comprise:.

For detecting and monitoring the angular displacements of the axes X1, X2 and X3, again at the nodal points B, C and D, the means <NUM> of detection and monitoring comprise:.

With such means of detection and monitoring <NUM>, linear and angular displacements are detected of the three axes X1, X2 and X3 with the minimum of components.

The PSD optical sensors and the laser emitters are managed by corresponding electronic boards.

Such electronic boards are connected by way of a digital communication channel to a central control and management unit that conducts the actual communication with the CNC (Computer Numerical Control) of the machine tool <NUM>.

Each electronic board has, on board, a controller for functionality and switching-on upon logical command of the central control and management unit, such central control and management unit also handling diagnostics and the supervision of the entire system.

The central control and management unit can directly program each single electronic board in order to set parameters such as the sampling time and the number of samples to carry out for each acquisition.

There are four logical operating modes, which are the following:.

The values used are always those in output from the boards on board the optical sensors, therefore they are the result of an average of one second of acquisition.

The scope of this mode is to give feedback on the state of the machine in a short time and in a form that is easily comparable with the calibration, hence the reason for the comparison in the same points.

All the electronic boards that manage the sensors carry out the analog/digital conversion of the necessary signals directly and transfer the data by way of the communication channel.

The electronic boards carry out the acquisition of the corresponding signals every time the central unit sends an acquisition command, responding with the digital value of the acquired signal.

The number of samples to be taken during the acquisition will be established directly by each card on the basis of the programming data sent by the central unit before starting acquisition mode.

It is possible to check for and download updates of the software used directly, by way of the CNC of the machine tool <NUM>, since the CNC can operate as the server of an internal local network, and by way of adapted commands it is also possible to receive the operation status of the detection and monitoring means <NUM>.

The control and management unit of the detection and monitoring means <NUM> interfaces with the CNC, at each sampling time providing the series of data detected.

A program loaded in the CNC manages the data and carries out the necessary dimensional compensation.

The control and management unit of the detection and monitoring means <NUM> is further provided with a calibration and self-diagnosis procedure, which interfaces directly with the CNC.

The control system sensors can be connected to the CNC through an Ethernet.

It is preferable that in each electronic board of each individual optical sensor the analog/digital conversion is performed directly, and that all the sensors interface with the electronic control and management unit by way of digital data, so as to reduce problems owing to analog errors, in order to decrease the number of wires necessary, and in order to obtain simple operations for maintenance and assistance.

The data corresponding to the dimensional deviations and to the deformations of the parts of the machine tool <NUM> are adapted to be used for operations to compensate such deviations and deformations.

The activity of automatically compensating mechanical deformations of the machine tool <NUM> follows the following operating method:.

In a second embodiment of the machine tool according to the invention, designated with the reference numeral <NUM> in <FIG>, and illustrative of a dedicated solution of a peculiar case in which only one item is to be detected, which is the linear deviation of a single reference nodal point B, referred to a first part <NUM> of the machine <NUM>, in turn corresponding to a controlled axis X1, with respect to a reference nodal point A associated with the footing <NUM>, the optical means <NUM> for detecting and monitoring the position of one or more of the controlled axes X1, X2, X3 comprising only one device <NUM> for detecting the translation of the nodal point B, along two axes, X2 and X3, which are perpendicular to the controlled axis X1.

Such device <NUM> for detecting the translation of a controlled axis comprises an emitter of a laser beam <NUM>, which is adapted to be fixed to the footing <NUM>, and referable to the first nodal point A, and an element for receiving the light signal, for example an optical position sensor <NUM>, which is integral with the second part <NUM> and referable to the second nodal point B.

In a third embodiment of the machine tool according to the invention, designated with the reference numeral <NUM> in <FIG>, and illustrative of a dedicated solution of a peculiar case in which two items are to be detected, which are the linear deviations of two reference nodal points B and C for two corresponding parts of the machine and for the respective controlled axes, the optical means of detecting and monitoring <NUM> comprising a first device <NUM> for detecting the translation of the axis X1, along two axes, X2 and X3, which are perpendicular to the controlled axis, and a second device 21a for detecting the translation of the axis X2, along two axes, X1 and X3, which are perpendicular to the controlled axis.

As an alternative, in order to control the linear deviations of two axes, it is possible to have one device <NUM>, as shown in <FIG>, for simultaneously detecting the translation of two mutually perpendicular controlled axes, for example the axis X1 and the axis X2.

In a fourth embodiment of the machine tool according to the invention, designated with the reference numeral <NUM> in <FIG>, and illustrative of a dedicated solution of a peculiar case in which the items to be detected are the linear deviations of three nodal points B, C and D, the optical means of detecting and monitoring <NUM> comprising a device <NUM> for simultaneously detecting the translation of three mutually perpendicular controlled axes, as described above.

Of such device <NUM> for simultaneously detecting the translation of three controlled axes, <FIG> shows:.

In a fifth embodiment of the machine tool according to the invention, designated with the reference numeral <NUM> in <FIG>, the detection and monitoring means <NUM> comprise a first device <NUM> for detecting the rotation of the axis X2, about two axes, X1 and X3, which are perpendicular to that controlled axis, a second device 26a for detecting the rotation of the axis X3, about two axes, X1 and X2, which are perpendicular to that controlled axis, a device <NUM> for detecting the translation of the axis X2 with respect to two axes X1 and X3 which are perpendicular thereto, and a device <NUM> for detecting the translation of the controlled axis X3, with respect to which the machining head <NUM> slides, along two axes that are mutually perpendicular X1 and X2.

In such fifth embodiment of the machine tool according to the invention, the reference device <NUM> is integral not with the footing <NUM> but with the second part <NUM> of the machine tool <NUM>, therefore a first reference nodal point is constituted by the nodal point B referred to the second part <NUM> of the machine, a second reference nodal point is constituted by the reference nodal point C for the third part <NUM> of the machine, and a third reference nodal point is constituted by the reference nodal point D for the machining head <NUM>; such solution is practicable if, for example, the first part <NUM> is integral with the footing <NUM> and structured so that its deformations are substantially negligible or fully detectable by way of the means of checking the position which are already integrated in the machine tool <NUM>.

It should be understood that the subject matter of the invention includes all the combinations of the devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> described above, as well as any variations of embodiment that are similar and equivalent, according to the deformations that it is desired to detect and monitor.

In a sixth embodiment thereof, a machine tool according to the invention is shown schematically in <FIG> and designated therein with the reference numeral <NUM>.

The machine tool <NUM> is of the portal type, with a first part <NUM> which is constituted by two opposing shoulders 512a and 512b which are fixed to the footing <NUM>, a second part <NUM> being arranged on each shoulder so as to slide along a first controlled axis X1 and being constituted by two opposing turrets 514a and 514b, which can slide in a parallel arrangement on the two shoulders 512a and 512b, which support a crossmember 514c.

A third part <NUM> slides along a second controlled axis X2 on the crossmember 514c, and is constituted for example by a slider, supporting the machining head <NUM> which is adapted to translate along a third axis X3.

The detection and monitoring means <NUM> comprise first means 519a for detecting and monitoring the deformations of the shoulders 512a and 512b, and second means 519b for detecting and monitoring the deformations of the crossmember 514c and of the machining head <NUM>.

The first detection and monitoring means 519a are shown for the purposes of example, in a first variation of embodiment thereof, in <FIG>, where a first shoulder 512a is shown schematically, it being understood that the opposing second shoulder 512b is arranged in the same way.

Such first detection and monitoring means 519a comprise two devices <NUM> and 21a for detecting the translation of the points where the corresponding optical sensor <NUM> and 23a is applied with respect to the points where the corresponding laser emitter <NUM> and 22a is positioned, these last items being integral with the footing <NUM>.

The two devices for detecting the translation <NUM> and 21a are positioned so as to operate with parallel laser beams, proximate to the lateral edges of each shoulder 512a and 512b.

On the basis of the deviation data detected for the two shoulders 512a and 512b, a first reference nodal point is determined to which to refer the deformations of the remaining second <NUM> and third <NUM> parts of the machine tool <NUM>, i.e. the deviations and the rotations of the other reference nodal points.

The first detection and monitoring means are shown for the purposes of example, in a second variation of embodiment thereof, in <FIG>, where they are generically designated with the reference numeral 619a and where a first shoulder 512a is shown schematically, it being understood that the opposing second shoulder 512b is arranged in the same way.

Such first means 619a comprise a single laser emitter <NUM>, a deflector that partially transmits the light beam <NUM>, and two optical sensors <NUM> and <NUM>, similarly to what is described above for the device <NUM> for detecting and monitoring the translations of two axes, plus a reflector <NUM> adapted to deflect the light beam <NUM>°.

The laser emitter <NUM>, integral with the footing at a first lower corner of the shoulder 512a, emits a beam toward a first optical sensor <NUM> arranged proximate to the upper corner of the shoulder 512a, above the laser emitter <NUM>.

The deflector that partially transmits the light beam <NUM> deflects a part of the light beam toward the reflector <NUM> positioned at the second lower corner of the shoulder 512a; the deflector <NUM> deflects the light beam toward the second optical sensor <NUM>, positioned proximate to the upper corner of the shoulder 512a above the reflector <NUM>.

Such first means 619a have one laser emitter less with respect to the first means 519a.

The second detection and monitoring means 519b comprise a device for simultaneously detecting the translation of two mutually perpendicular controlled axes, i.e. the axis X2 and the axis X3, as described above, i.e. comprising:.

In particular, with the invention a machine tool has been devised with which it is possible to determine with precision the deviations of the machining head with respect to the specified operating positions and trajectories, so as to be able to correct them, thus periodically restoring the necessary operating precision to the machine.

Furthermore, with the invention an apparatus has been devised to determine such deviations.

Moreover, with the invention a machine tool has been devised which is rapidly adaptable to the environmental and vibrational conditions of operation, thanks to the capacity to detect linear deviations and structural angular deviations, due also to environmental and vibrational conditions, and hence to compensate for such deviations.

The invention, thus conceived, is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

Claim 1:
A Cartesian numerically controlled machine tool (<NUM>) for high-precision machining, comprising:
- a footing (<NUM>),
- a first part (<NUM>; <NUM>) with first movement means (<NUM>) for the movement of a second part (<NUM>; <NUM>) with respect to a first controlled axis (X1), said first part (<NUM>; <NUM>) being mounted on said footing (<NUM>);
- a second part (<NUM>) with second movement means (<NUM>) for the movement of a third part (<NUM>; <NUM>) with respect to a second controlled axis (X2),
- the third part (<NUM>; <NUM>) with third movement means (<NUM>) for the movement of a machining head (<NUM>) with respect to a third controlled axis (X3),
- a machining head (<NUM>; <NUM>),
- at least one reference nodal point (A, B, C, D) for each of one or more of said controlled axes (X1, X2, X3) with respect to a reference device (<NUM>) that is integral with a part of said machine tool (<NUM>),
wherein a reference nodal point (A) is established on said footing (<NUM>), a reference nodal point (B) is established on said first part (<NUM>; <NUM>), a reference nodal point (C) is established on said second part (<NUM>) and a reference nodal point (D) is established on said third part (<NUM><NUM>; <NUM>),
- -on board, optical means (<NUM>; <NUM>) for detecting and monitoring the position of the at least one reference nodal point (B, C, D) for each of one or more of said controlled axes (X1, X2, X3) with respect to said reference device (<NUM>), said reference device (<NUM>) being integral with the footing (<NUM>) and being associated with the reference nodal point (A) established on the footing (<NUM>).