A UTOMA TIC SYSTEM DESCRIPTION

The present patent concerns portal machining centres, and in particular it concerns a new automatic system for correcting the position of tools in portal machining centres, for example of the gantry type, and the process of use of said automatic system.

Portal machining centres of the gantry type are known, meaning machining centres comprising a frame substantially in the shape of a portal, translating along a first horizontal direction, on which a carriage is mounted which in turn translates on said frame in a second horizontal direction that is orthogonal to said first direction. Said carriage is provided with a slide suited to ensure the vertical movement of the tool head that is mounted on it and that has one or more rotation axes and in turn is capable of orienting the tool in various ways.

In this way, by translating said portal frame, said carriage and said head-carrier slide it is possible to bring the tool bit in any position on a work table.

Once the tool has been positioned on the piece to be machined, which in turn is constrained to said work table, said tool head can variously incline the tool, which initially is positioned vertically, in one or more directions on vertical planes.

In order to perform the desired machining operations on a workpiece it is necessary to position the tool, to orient it precisely with respect to the workpiece and to have it cover a programmed path.

The precision of a machining cycle carried out on a portal machining centre of the gantry type is affected by several factors that can be due, for example, to: geometrical mechanical errors of various types, thermal creep and thermal gradient, settling of the foundations, limited accuracy of the linear and rotary measurement systems positioned on the work axes and other factors. All these errors mutually affect one another and cause a deviation of the actual position of the tool with respect to the ideal position of the machining tool along the programmed machining path.

This deviation of the actual machining point of the tool varies in a non- homogeneous manner within the work area, being affected by the factors mentioned above in a inconstant manner.

Therefore, during the machining cycle, it is not possible to know or foresee the actual position that will be assumed by the tool.

In order to overcome the drawbacks described above, a new type of automatic system and the process of use of the same have been designed and developed, wherein said automatic system is suited to correct the position of machining tools that are orientable in space, in portal machining centres, for example of the gantry type.

The main object of the present invention is to provide an automatic system that makes it possible to reduce errors in the positioning of the tool by controlling and correcting the actual position of the machining tool oriented in space.

It is another object of the present invention to automate said process for correcting the position of the tool, to the advantage of production times and of the precision of the final result.

It is another object of the present invention to make the tool position correction operation quicker and more reliable by subdivinding the work area in zones or quadrants.

These and other direct and complementary objects are achieved by the new automatic system for correcting the position of machining tools that are orientable in space, in portal machining centres, for example of the gantry type, and by the process of use of said automatic system.

The new automatic system is suited to be installed in machining centres, for example in portal machining centres of the gantry type, comprising a work area, at least one work table positioned on said work area and defining a fixing plane for the pieces to be machined, at least one portal frame translating with respect to said plane and to said table in at least one first horizontal direction, at least one carriage mounted on the crosspiece of said portal frame and suited to translate on said frame in at least one second horizontal direction that is orthogonal to said first direction, at least one tool head provided with one or more rotation axes and mounted on a slide that in turn is mounted on said carriage for the vertical translation of said head, the latter being suited to orient at least one tool with respect to said table and therefore with respect to the workpiece.

Said two horizontal translation directions of said frame and said carriage define the two horizontal Cartesian axes X and Y, while the vertical translation direction of said head on said slide defines the third vertical Cartesian axis Z.

The automatic system comprises at least one laser source suited to produce one or more laser beams, of which at least one laser beam oriented according to a first horizontal direction and at least one laser beam oriented according to a second horizontal direction orthogonal to the first one.

Preferably, said two horizontal directions of said two laser beams are respectively oriented so that they are parallel to said horizontal Cartesian axes X and Y of the machining centre.

The system, in fact, aligns the directions of said laser beams with the Cartesian coordinate system (X and Y axes) of the machining centre.

Said laser beams are precisely set and the direction and position of said laser beams is stored in the coordinate system of the machine.

Said at least two laser beams, referred to as transverse and longitudinal laser beams here below, preferably but not necessarily lie on the same horizontal plane at a given height on the Z-axis. In this case, said laser beams meet in one or more points, called reset points, which are located at respective known heights along the Z-axis. Said at least one laser source is, for example, of the stand-alone type. Alternatively, said at least one laser source can be connected to the electronic control system of the machining centre, in order to transmit the signal of interruption of said one or more laser beams when an object comes to be positioned in their trajectory.

According to a first possible embodiment, the new system may comprise one or more of said laser sources, each one of them being suited to generate said two or more laser beams oriented according to said two horizontal directions through a plurality of prisms with angular deviation.

According to a further possible embodiment, the new system may comprise a single laser source for each one of said laser beams.

Said laser beams, generated by said one or more laser sources, are used by the new system to detect the position of the tool during the machining cycle.

Usually, the tool head orients the tool in the vertical position, translates it on the workpiece and starts the machining cycle. It is known that when the tool needs to be inclined to carry out the programmed inclined machining operations on the workpiece the actual position of the tool bit may be different from the position programmed for the machining cycle.

The new system feels, that is detects, and corrects the position of said variously oriented tool as described and claimed here below.

In order to feel the position of said tool, the tool bit is translated until it intersects one of the laser beams oriented according to a first direction, for example said longitudinal laser beam, thus determining with certainty the actual position of the tool on the X-axis, and calculating the error between the hypothetical X-coordinate and the actual X-coordinate of the tool.

The tool then needs to be translated until its bit intersects said second transverse laser beam, thus determining with certainty also the actual position of the tool on the Y-axis, and calculating the error between the hypothetical Y-coordinate and the actual Y-coordinate of the tool. Analogously, the tool then needs to be translated in the vertical direction until its bit intersects said first or said second transverse laser beam, thus determining with certainty also the actual position of the tool on the Z-axis, and calculating the error between the hypothetical Z-coordinate and the actual Z-coordinate of the tool. In this way, the machining tool can be started again, any positioning errors having been reset or in any case calculated.

In particular, said one or more laser sources are suited to form at least two of said transverse laser beams and at least two of said longitudinal laser beams, defining a reference quadrant that preferably and substantially coincides with the perimeter of the work area.

According to said first solution, the new system comprises a single laser source that is deviated through a plurality of angular prisms to form said laser beams.

According to said second solution, the new system comprises at least two of said laser sources suited to emit the laser beams oriented according to the longitudinal direction, meaning parallel to the X-axis, and at least two of said laser sources suited to emit the laser beams oriented according to the transverse direction, meaning parallel to the Y-axis, thus generating at least four laser beams parallel to each other in pairs, and four points of intersection, said four laser beams lying on a single horizontal plane at a given height along the Z-axis.

In order to optimize the error reset process, it is possible to translate the tool towards the nearest laser beams, keeping into account the orientation of the tool. Considering that said four points of intersection between said laser beams define four quadrants, it is furthermore possible for the system to translate the tool towards the laser beams positioned in the quadrant that is located in the direction of inclination of the tool and/or in the quadrant where the machining operation is being performed.

The new system can furthermore comprise one or more sets of said sources of said transverse and longitudinal laser beams positioned at different heights, so as to determine various positions along the Z-axis.

Therefore, the new system allows a sort of "reference square" to be obtained with said laser beams, in which it is possible to verify the errors in the positioning of the machining tool oriented in space in each one of said positioning quadrants.

The process of use of the new system comprises a first cycle referred to as reset and compensation cycle of the tool oriented in space, said cycle being performed when necessary.

Said first cycle includes the check of the actual position of the tool bit on the three axes X, Y, Z, which is performed by translating said tool, arranged vertically, so that its bit meets first one of said longitudinal laser beams, defining the first actual X-coordinate, then one of said transverse laser beams, defining the second actual Y-coordinate, and wherein the actual Z-coordinate is given by the height of said laser beams intersected by the tool bit, said height being determined by moving said tool itself in the vertical direction until it intersects one of said laser beams. The cycle then comprises the step of inclination of the head by a given angle, which is carried out orienting said tool in a corresponding manner.

With the tool oriented, the operation of determining the actual position of the tool bit is repeated, successively translating the tool on one of said longitudinal laser beams and on one of said transverse laser beams, and then determining the coordinates X, Y, Z.

The tool positioning error is calculated by comparing the values obtained from the two checks, and therefore the respective compensation, calculated automatically by the numerical control of the machining centre, can be applied.

The process of use of the new system comprises also a so-called dimensional thermal setting cycle intended to compensate for the errors ascribable to temperature variations, said cycle being performed when necessary.

The supports of said laser sources and of any deviation prisms are preferably provided with one or more thermal probes suited to detect and compensate for any possible thermal creep of the supports themselves.

Said thermal setting cycle is thus carried out by comparing the data related to the position of the tool bit with the reference points of the previously set laser beams. The error found will thus be used to calculate the compensation.

The characteristics of the new system will be highlighted in greater detail in the following description with reference to the attached drawings which are enclosed hereto by way of non-limiting example.

Figure 1 shows a schematic view of a machining centre (C) of the portal type.

Figure 2 shows a schematic plan view of the new system (1) for correcting the position of a tool (U) of a machining centre (C) of the portal type, in which it is possible to observe the reference square (Q) formed by four laser beams (Lxl, Lx2, Lyl, Ly2) parallel to each other in pairs.

Figure 3 shows a schematic front view of the new system (1) for correcting the position of a tool (U) of a machining centre (C) of the portal type, in which it is possible to observe the laser sources (Sxl, Sx2, Syl, Sy2). According to the invention, the new system (1) may in any case comprise at least one laser source whose beam is then deviated several times through angular prisms in order to generate said laser beams (Lxl, Lx2, Lyl, Ly2).

The invention is a new automatic system (1) for correcting the position of the machining tools (U) that can be oriented in space used in portal machining centres (C), for example of the gantry type.

The machining centre (C) is of the type comprising at least one work table (T), at least one portal frame (CI) translating with respect to said table in a first longitudinal horizontal direction (X) or X-axis, at least one carriage (C2) mounted on said portal frame (CI) and translating on said frame (CI) in a second transverse horizontal direction (Y) or Y-axis, orthogonal to said first longitudinal direction (X), at least one tool head (C4) mounted on a slide (C3) suited to translate in the vertical direction (Z) and in turn mounted on said carriage (C2). Said tool head (C4) is of the type with one or more rotation axes and is suited to orient at least one tool (U) with respect to said table (T) and therefore with respect to the piece to be machined.

In a first solution, the automatic system (1) comprises at least one single laser source (Sxl) and a plurality of deviation prisms suited to produce at least two laser beams (Lxl, Lx2) oriented according to the longitudinal direction parallel to said X-axis of the machining centre (C) and at least two laser beams (Lyl, Ly2) oriented according to the transverse direction parallel to said Y-axis of the machining centre (C).

In a second solution, illustrated also in the drawings, the automatic system (1) comprises:

• at least two laser sources (Sxl, Sx2), each one of which is suited to emit a laser beam (Lxl, Lx2) oriented according to the longitudinal direction parallel to said X-axis of the machining centre (C);

• at least two laser sources (Syl, Sy2), each one of which is suited to emit a laser beam (Lyl, Ly2) oriented according to the transverse direction parallel to said Y-axis of the machining centre (C).

In this way, with said first solution or with said second solution, four laser beams are defined which are parallel to each other in pairs, as well as four points of intersection (1, 2, 3, 4), said four laser beams preferably lying on a single horizontal plane at a given height along the Z-axis.

Therefore, the new system makes it possible to obtain a sort of "reference square " (Q) with said laser beams (Lxl, Lx2, Lyl, Ly2).

As shown in Figure 2, the tool head (C4) can orient the tool (U) in a vertical direction (right side) or in a generally inclined direction with respect to the vertical direction (Z) (left side).

Considered that said four points of intersection (1, 2, 3, 4) between said laser beams (Lxl, Lx2, Lyl, Ly2) define four quadrants (Ql, Q2, Q3, Q4), according to the invention the system may provide for translating the tool (U) towards the laser beams (Lxl, Lx2, Lyl, Ly2) positioned in the quadrant (Ql, Q2, Q3, Q4) that lies in the direction of inclination of the tool (U) and/or in the quadrant where the machining operation is being performed.

The new system may furthermore comprise several of said single sources (Sxl) with deviation prisms or several sets of said sources (Sxl, Sx2, Syl, Sy2) of said longitudinal laser beams (Lxl, Lx2) and transverse laser beams (Lyl, Ly2) positioned at different heights to determine various positions along the Z-axis. These are the schematic outlines that are sufficient to the expert in the art to carry out the invention, consequently upon implementation variants may be developed that do not affect the substance of the innovative concept introduced herein.

Therefore, with reference to the above description and the attached drawings, the following claims are expressed.