Patent Description:
The invention has its preferred application in a computerized numerical control (CNC) milling machine having members that are movable along coordinated axes in order to move a milling tool within a work volume, to which reference will be made in the description below without because of this loosing in generality.

In the last decades, CNC milling machines were developed, which are provided with movable members with different degrees of freedom, so as to allow for a great flexibility in the machining of a piece to be processed. In particular, known milling machines can be programmed so as to carry out a wide range of different machining operations, depending on special needs.

Documents <CIT>, <CIT> and <CIT> disclose respective examples of milling machines and documents <CIT> and <CIT> disclose respective high-precision drive and transmission assembly to avoid backslashes. The machine tool of <CIT> comprises two carriages arranged at a fixed distance with respect to each other and slidable together along a guide element; and a slide interposed between the two carriages, carried by the two carriages and slidable in relation to the two carriages; wherein said carriages are independent and mechanically linked together solely by said slide.

In order to fulfil the requirements mentioned above, known milling machines comprise a plurality of members that are movable according to coordinated axes. These members can comprise, for example, a carriage that can slide along a guide in a first direction, for example a horizontal one, and a slide carried by the carriage in a projecting manner and movable, relative to the latter, along a second direction perpendicular to the first direction, for example a vertical one.

Hence, the carriage typically has a "cross-like" shape, since it has, on a first face of its, a first seat along an axis for the coupling to the guide and, on a second face of its opposite the first one, a second seat orthogonal to the first seat for the coupling to the slide.

Since the two seats cannot intersect one another, this necessarily leads to a projecting arrangement of the slide (and, hence, of the milling head) relative to the guide of the carriage. As a consequence, the weight of the carriage and of the slide, as well as the forces exchanged with the piece during the machining, determine significant bending moments relative to the guide, with potentially negative effects on the machining precision. In order to avoid these effects, the members of the machine need to be properly sized so as to ensure the necessary stiffness thereof, which leads to an increase in the weight and in the cost of the components as well as to dynamic problems.

The object of the invention is to at least partly overcome the drawbacks of the prior art.

In particular, the object of the invention is to provide a lighter machine tool with a smaller cost, which is capable of carrying out high-speed machining operations, ensuring at the same time a suitable quality of the machining.

According to the invention, there is provided a machine tool comprising:.

Thanks to the invention, the bending moment acting upon the guide element is limited by the fact that the slide is arranged between the two carriages and, hence, can be placed close to the guide element.

In this way, the guide element and the relative support structure are not subjected to significant deformations, thus ensuring better performances in terms of machining precision.

Alternatively, the required precision being the same, the weight and the cost of the machine can be reduced.

Furthermore, thanks to the fact that the two carriages are independent of one another, by controlling the sliding of the two carriages along the guide element it is possible to ensure an adequate stiffness of the machine in order to fulfil requirements set by different operating conditions.

Basically, during rough-milling operations involving great forces, the two motors are controlled so as to exert opposite torques with a high modulus upon the respective toothed wheels so as to obtain a high-stiffness connection between the carriages and the slide.

During superficial finishing operations involving smaller forces, the two motors are configured to exert opposite torques with a smaller modulus upon the respective toothed wheels so as to obtain a connection between the carriages and the slide with a smaller stiffness, thus limiting wear.

The technical advantages described above are more evident in large-sized machine tools designed according to the invention.

According to a preferred embodiment of the invention, the slide carries a machining head.

According to an embodiment of the invention, the guide element comprises at least one rail extending in a direction parallel to the first axis and each one of the carriages comprises at least one runner coupled to the rail in a sliding manner along the direction of the first axis and in a rigid manner in a direction perpendicular to the first axis.

In this way, the space taken up by the guide system is minimized, since the guide system does not require further constraint elements in the other directions.

In particular, the slide comprises a second rack extending in a direction substantially parallel to the second axis; at least one of the two carriages comprising at least one motor provided with a toothed wheel, which meshes with the second rack so as to control the sliding of the slide along the second rack.

In particular, one of the two carriages comprises a third motor and a fourth motor, which are provided with respective toothed wheels, which mesh with the second rack and are configured to exert respective torques in opposite direction upon the respective toothed wheels.

In this way, the clearances of the coupling between the toothed wheels and the second rack can be limited and a suitable precision in the movement of the slide can be ensured.

Alternatively, one of the two carriages comprises a third motor and the other one of the two carriages comprises a fourth motor, said third and fourth motor being provided with respective toothed wheels, which mesh with the second rack and are configured to exert respective torques in opposite directions upon the respective toothed wheels.

In this configuration, the clearances between the toothed wheels and the rack are limited by the weight force of the slide.

Further features and advantages of the invention will be best understood upon perusal of the following description of a non-limiting embodiment thereof, with reference to the accompanying Figures, wherein:.

With reference to <FIG> and <FIG>, number <NUM> indicates, as a whole, a machine tool, in particular a milling machine, preferably a CNC milling machine. The milling machine <NUM> comprises a substantially straight guide element <NUM> extending along an axis A1, for example a horizontal one; two carriages <NUM> and <NUM>, which are arranged at a fixed distance D from one another along the guide element <NUM> and are capable of sliding together along the guide element <NUM>; a slide <NUM>, which is interposed between the carriages <NUM> and <NUM>, is carried by the carriages <NUM> and <NUM> and can slide relative to the carriages <NUM> and <NUM> along an axis A2 perpendicular to the axis A1, in particular a vertical one; and a milling head <NUM>, which is carried by the slide <NUM> and is configured to carry a milling tool (which is not shown in the accompanying Figures).

The guide element <NUM> is supported by a fixed or movable support structure, which is not shown in the accompanying figures because it is not part of the invention. In particular, said support structure can assume different configurations. By way of example, the support structure comprises two vertical supports, each fixed to a respective end of the guide element <NUM>, so as to define a gantry milling machine <NUM>.

With reference to <FIG>, the guide element <NUM> comprises a rail <NUM> and a rail <NUM>, each extending in a direction that is substantially parallel to the axis A1. In particular, the rails <NUM> and <NUM> have a section shaped like a dovetail.

According to a variant of the invention, which is not shown in the accompanying Figures, the guide element <NUM> can comprise only one rail extending in a direction parallel to the axis A1. The number of rails of the guide element <NUM> can change and is not limited by the invention.

With reference to <FIG> and <FIG>, the guide element <NUM> comprises a rack <NUM> extending in a direction that is parallel to the axis A1 and, hence, parallel to the rails <NUM> and <NUM>.

With reference to <FIG>, <FIG> and <FIG>, each one of the carriages <NUM> and <NUM> comprises four runners <NUM>, two of them being configured to slide on the rail <NUM> and the other two being configured to slide on the rail <NUM>. In particular, each runner <NUM> is shaped so as to be coupled to the dovetail-shaped section of the rails <NUM> and <NUM> in a sliding manner along the direction of the axis A1 and in a rigid manner in the directions orthogonal to the axis A1, so as to only allow the carriages <NUM> and <NUM> to slide along the rails <NUM> and <NUM> and avoid the relative movement of the carriages <NUM> and <NUM> relative to the guide element <NUM> in all other directions.

According to a variant of the invention, which is not shown in the accompanying Figures, each carriage <NUM> and <NUM> is provided with only two runners <NUM>, one of them being configured to slide on the rail <NUM> and the other one being configured to slide on the rail <NUM>. The number of runners <NUM> of the two carriages <NUM> and <NUM> can change and is not limited by the invention.

With reference to <FIG>, the carriage <NUM> comprises an electric motor <NUM> and the carriage <NUM> comprises an electric motor <NUM>. Each electric motor <NUM>, <NUM> is provided with a respective toothed wheel <NUM> (<FIG> and <FIG>), which meshes with the rack <NUM> (<FIG> and <FIG>).

In particular, the motors <NUM> and <NUM> are configured to exert respective torques in opposite directions upon the respective toothed wheels <NUM> (<FIG> and <FIG>) so as to limit the clearances of the coupling between the toothed wheels <NUM> (<FIG> and <FIG>) and the rack <NUM> (<FIG> and <FIG>).

With reference to <FIG>, the slide <NUM> is oblong in the direction A2, has a substantially rectangular section and comprises at least two rails <NUM> and <NUM>, each facing the respective carriage <NUM>, <NUM> and extending in a direction that is parallel to the axis A2. In particular, the rails <NUM> and <NUM> have a section shaped like a dovetail.

Each carriage <NUM>, <NUM> comprises at least one slider <NUM>, which is configured to slide along the respective rail <NUM>, <NUM>. In particular, each slider <NUM> is shaped so as to be coupled to the dovetail-shaped section of the rails <NUM> and <NUM> in a sliding manner along the direction of the axis A2 and in a rigid manner in the directions orthogonal to the axis A2, so as to only allow the slide <NUM> to slide along the axis A2 and avoid the relative movement of the slide <NUM> relative to the carriages <NUM> and <NUM> in all other directions.

In the specific case described and shown herein, the slide <NUM> comprises two rails <NUM> and two rails <NUM>. The carriage <NUM> comprises eight sliders <NUM>, four of them being configured to slide on one of the two rails <NUM> and four of them being configured to slide on the other one of the two rails <NUM>. The carriage <NUM> comprises eight sliders <NUM>, four of them being configured to slide on one of the two rails <NUM> and four of them being configured to slide on the other one of the two rails <NUM>. The number of rails <NUM> and <NUM> and of sliders <NUM> can change and is not limited by the invention.

With reference to <FIG>, the slide <NUM> comprises two racks <NUM>, each extending in a direction that is parallel to the axis A2 and, hence, parallel to the rails <NUM> and <NUM>.

Furthermore, the carriage <NUM> comprises an electric motor <NUM> and the carriage <NUM> comprises an electric motor <NUM>. Each electric motor <NUM>, <NUM> is provided with a respective toothed wheel <NUM>, which meshes with the respective rack <NUM>.

In particular, the motors <NUM> and <NUM> are configured to exert respective torques in opposite directions upon the respective toothed wheels <NUM> so as to limit the clearances of the coupling between the toothed wheels <NUM> and the rack <NUM>.

According to a variant of the invention, which is not shown in accompanying Figures, the sole carriage <NUM> comprises a motor.

With reference to <FIG>, the milling head <NUM> comprises two bodies <NUM> and <NUM>, which are articulated to one another, and a milling tool, which is carried by the body <NUM> and is not shown in the accompanying Figures.

In particular, the body <NUM> is connected to the slide <NUM> so as to rotate relative to the slide <NUM> around the axis A2 and the body <NUM> is connected to the body <NUM> so as to slide relative to the body <NUM> around an axis A3 that is perpendicular to the axis A2.

Furthermore, the milling head <NUM> comprises motors and/or actuators, which are not shown in the accompanying Figures and are configured to move the bodies <NUM> and <NUM> and to start the rotation of the milling tool, which is not shown in the accompanying Figures.

In <FIG>, the axis A1 of the guide element <NUM> is horizontal and the axis A2 is vertical; according to a variant of the invention, which is not shown in the accompanying Figures, the axis A1 could be vertical and the axis A2 could be horizontal.

In use and with reference to <FIG>, the motors <NUM> and <NUM> start the sliding of the carriages <NUM> and <NUM> along the guide element <NUM>. In particular, in order to start the sliding of the carriages <NUM> and <NUM> in a first direction, the power of one of the motors <NUM> and <NUM> is increased so as to increase the torque of one of the two motors <NUM> and <NUM> compared to the other one of the two motors <NUM> and <NUM>. In order to start the sliding of the carriages <NUM> and <NUM> in a second direction, which is contrary to the first direction, the power of the other one of the two motors <NUM> and <NUM> is increased.

In particular, the motors <NUM> and <NUM> control, in a coordinated manner,
the torques exerted upon the respective toothed wheels <NUM> so as to modulate the stiffness of the connection between the carriages <NUM>, <NUM> and the slide <NUM> depending on the forces involved.

Similarly, the motors <NUM> and <NUM> start the sliding of the slide <NUM> relative to the carriages <NUM> and <NUM> in the direction of the axis A2.

The bodies <NUM> and <NUM> are oriented so as to move the milling tool, which is not shown in the accompanying Figures, within a work volume based on the specific machining needs.

<FIG> shows a variant in which the slide <NUM> has a tapered section, instead of a substantially rectangular one; therefore, the two rails <NUM> and the two rails <NUM> on the opposite sides of the slide <NUM> are not coplanar to one another, but are staggered in a direction parallel to the axis A1. The carriages <NUM>, <NUM> are shaped in a corresponding manner, on their side facing the slide <NUM>, and the sliders <NUM> of each carriage <NUM>, <NUM> are arranged on planes which, in turn, are staggered in order to cooperate with the corresponding rails <NUM> or <NUM>.

Finally, the invention can evidently be subjected to further variants to the embodiments described herein, though without going beyond the scope of protection set forth in the appended claims.

Claim 1:
Machine tool comprising:
- a substantially straight guide element (<NUM>) extending along a first axis (A1) and comprising a first rack (<NUM>) extending in a direction parallel to the first axis (A1);
- two carriages (<NUM>, <NUM>) arranged at a fixed distance (D) with respect to each other along the guide element (<NUM>) and slidable together along the guide element (<NUM>), at least one of the two carriages (<NUM>, <NUM>) comprising at least one motor (<NUM>; <NUM>) fitted with a toothed wheel (<NUM>) which engages with the first rack (<NUM>); and
- a slide (<NUM>) interposed between the two carriages (<NUM>, <NUM>), carried by the two carriages (<NUM>, <NUM>) and slidable in relation to the two carriages (<NUM>, <NUM>) along a second axis (A2) perpendicular to the first axis (A1);
wherein said carriages (<NUM>, <NUM>) are independent and mechanically linked together solely by said slide (<NUM>);
wherein one of the two carriages (<NUM>, <NUM>) comprises a first motor (<NUM>) and the other of the two carriages (<NUM>, <NUM>) comprises a second motor (<NUM>), the first and second motors (<NUM>, <NUM>) being fitted with respective toothed wheels (<NUM>) which mesh with the first rack (<NUM>) and are configured to exert respective torques in opposite directions upon the respective toothed wheels (<NUM>); and
wherein the first and the second motor (<NUM>, <NUM>) are configured to control, in a coordinated manner, the torques exerted upon the respective toothed wheels (<NUM>) so as to modulate the stiffness of the connection between the carriages (<NUM>, <NUM>) and the slide (<NUM>) in a direction substantially parallel to the first axis (A1).