"Machine tool or work centre for pieces made of wood and the like"

DESCRIPTION Technical field

The present invention relates to improvements to machine tools or work centers for machining pieces made of wood, light metals, plastic, or the like, using tools for chip removal.

More in particular, the present invention relates to improvements to machines or work centers of the so-called "open-bridge" or "cantilever" or "arm- machine" type. State of the art

In the field of machine tools for machining wood and other light materials, machine tools or work centers of the so-called "arm-machine" or "open-bridge" type are used, in which an upright moves, along a first numeric-control axis of translation, on a machine bed or base provided with rectilinear guides. Said upright carries an approximately horizontal arm with a second guide, oriented in a direction orthogonal to the first guide set on the machine bed. Mobile on the second guide, along a second numeric-control axis of translation, is a carriage, which is in turn equipped with a third guide, orthogonal or approximately orthogonal to the first and second guides. Mobile on the third guide, along a third numeric-control axis of translation, is a slide, which carries an operating or machining head with one or more tool chucks.

The above machines carry out machining of pieces that are located in a space set alongside the base or machine bed, or else on an area of the base or machine bed set alongside the area in which the guides for translation of the upright carrying the head are arranged. In this case, the machine bed will have a larger width.

Figures 1 and 2 show a schematic embodiment of a machine tool or work center of an open-bridge type, as described above and in itself substantially known. Designated by 1 is the base, anchored to a floor PP and developing in a substantially horizontal direction. Set on the base 1 is a guide 3, constituted, in the example illustrated, by two parallel rails. Mobile on the guide 3, along a first numeric-control axis X, is an upright 5, which develops vertically above the base 1. '

The upright 5 carries at the top an approximately horizontal arm 7, set on

which is a second, substantially horizontal, guide 9, constituted by a pair of rails. Translating on the guide 9, along a numeric-control axis Y, is a carriage 11 , oh which a third guide 13 is provided, which is also constituted in this case by rails substantially parallel to one another and extend in a direction Z orthogonal to the direction X and to the direction Y, i.e., in a vertical direction of translation. Moving in said substantially vertical direction, along a third numeric- control axis Z, is a slide 14. The latter carries a machining or operating head 15, which, in the example shown, comprises a single chuck 17. with a pair of opposed and coaxial tools U1 , U2. The chuck 17 can rotate about a numeric- control axis of oscillation or rotation designated by A. The head 15 can be provided with a further movement of rotation or oscillation as indicated by the double-headed arrow B about a vertical axis.

Each of the movements along the numeric-control axes X, Y and Z is controlled via an electronic-control motor and suitable transmission systems, for example, of the external-screw/internal-screw type, not shown in so far as they are known to those skilled in the art.

Figures 1 and 2 illustrate also a second arrangement of the chuck, arm, carriage, slide, and operating head that is symmetrical to the arrangement 5, 7, 9, 11, 13, 14, 15. In effect, these machines can be equipped with two symmetrical uprights, although this is not strictly necessary.

As may be noted from the configuration illustrated with reference to Figures 1 and 2, the pieces to be machined (designated as a whole by P), can be set on a support S (Figure 2), located on one side of the base 1. Basically, then, in these machines usually the pieces P to be machined are stationary, whilst the chuck or chucks are provided with a numeric-control movement along three axes of translation X, Y, Z and possibly about one or two numeric- control .axes of oscillation A, B.

Designated by M in Figures 1 and 2 is the centroid of the upright 5, designated by B is the centroid 'of the arm 7, and designated by MA is the axis of symmetry or trace of the plane of symmetry of the upright 5, on which the centroid M of the upright itself lies.

The accelerations in the direction' bf the numeric-control axis X generate remarkable stresses on the structure of the machine, with consequent elastic deformations that result in undesirable displacements of the chuck or chucks.

Said displacements are designated by ηx in the figures. These displacements lead to dimensional errors in the machining operation. All the other conditions being equal, the undesirable displacements ηx of the chuck or chucks are the greater, the further the carriage 11 with the slide 14 and the head 15 are displaced towards the distal end of the arm 7, i.e., the end projecting in cantilever fashion from the upright 5. In fact, all the other conditions being equal, the displacements ηx of the chuck 17 determined by the accelerations along the numeric-control axis X directly depend upon the static moments of the various masses of the arm 7, of the carriage 11 , of the slide 14, and of the head 15 with respect to the median axis MA of vertical symmetry of the upright 5.

If YB is the distance between the axis of vertical symmetry MA of the upright 5 and the centroid B of the arm 7 and MB is the mass of the arm 7 itself, the static moment of the latter is given by ^{" '} MB x YB

•Said static moment is very important, since the arm 7 has a mass directly dependent upon the amount of the travel along the axis Y that can be assigned to the tools, and YB has a high value only slightly less than half of the travel itself along the axis Y. The static moment of the carriage 11 is given by

M11 x Y11 where Y11 is the distance of the centroid of the carriage 11 with respect to the median plane MA of the upright 5, and M11 is the mass of the carriage 11. The static moment of the slide 14 is given by M14 x Y14 where Y14 is equal to Y11 and is the distance between the centroid of the slide 14 and the median plane of trace MA of the upright 5, and M14 is the mass of the slide 14.

The elastic displacements ηx of the chuck depend, moreover, upon the elastic bending of the arm 7 in the plane XY, i.e., in the plane of Figure 1. Said elastic bending of the arm 7 is also due to the forces of inertia directed along the axis X and applied to the masses of the carriage 11 and of the slide 14 with the head carried thereon.

Also the mass of the arm 7 produces a displacement ηx that is the

greater, the greater the length of the arm itself.

It may be readily understood from the foregoing how the masses involved and their arrangement affect considerably the undesirable displacements ηx undergone by . the chuck or chucks of the machine following upon the accelerations along the numeric-control axis X.

Objects and summary of the invention

An object of the present invention is to provide a work centre or machine tool that will overcome totally or at least in part the drawbacks described above. The object of a particular embodiment of the invention is to provide a machine or work center, in which the masses of the various components are arranged in an optimal way to reduce the elastic deformations that lead to undesirable displacements of the tools on account of the accelerations along the numeric-control axis of translation X. The above and further objects and advantages, which will be evident to those skilled in the art from a reading of the ensuing text, are achieved basically with a work center or machine tool comprising:

> a base with a first guide for translation of at least one upright along a first numeric-control axis; > on said upright, an arm with a second guide for translation of a carriage along a second numeric-control axis; and

> on said carriage, a third guide for translation of a slide along a third numeric-control axis, carried on which is a machining head with at least one tool chuck; wherein:

> the arm extends on opposite sides of ' a vertical median plane of said upright; and

> the arm, the carriage, and the slide are configured for bringing the head into a working position beyond the end of the arm in the direction of the second axis of translation.

With the above configuration there is a reduction in the moments of inertia and hence in the elastic deformations of the elements of the machine with consequent improvement ^' in the machining quality. A more detailed discussion of the factors that contribute to reducing the elastic deformations

will be made with reference to a non-limiting example of embodiment of the invention.

According to a possible embodiment, the arm has a development approximately symmetrical with respect to said vertical median plane, the centrpid of said arm lying approximately on said vertical median plane of the upright.

Preferably, according to a possible embodiment, the third guide carried by said carriage is arranged on a substantially vertical plane, inclined with respect to a substantially vertical plane of sliding of said carriage, in such a way that the slide and the head project with respect to the carriage towards one end of said arm.

According to a modified embodiment, the third guide can assume positions that vary with respect to the carriage, for displacing the position of the third axis of translation and machine pieces arranged alternatively along one side or the other of the machine bed. Preferably, the third guide can move about a substantially vertical axis.

For example, the third guide can be provided on a slider that is able to move along arched guides, developing around a substantially vertical axis.

In a particularly advantageous embodiment, the third guide is mobile with respect to said carriage so as to assume at least two positions symmetrical with respect to a substantially vertical plane, thus enabling machining of pieces set on either side of said base.

According to another aspect, the invention relates to a work center or machine tool comprising: > a base with a first guide for translation of at least one upright along a first numeric-control axis;

> on said upright, an arm with a second guide for translation of a carriage along a second numeric-control axis; and

> on said carriage, a third guide for translation of a slide along a third numeric-control axis, on which a machining head is carried with at least one tool chuck; wherein:

> the arm extends on opposite sides of said upright; and

> the machining head can be set on the carriage inclined with respect to the

first axis of translation and to the second axis of translation, the travel of said carriage along said second axis being such as to be able to translate the machining head beyond at least one of the ends of said arm.

Further advantageous characteristics and embodiments are indicated in the attached claims.

Brief description of the drawings

The invention will be better understood with reference to the description and the attached drawings, which show practical non-limiting embodiments of the invention. More in particular, in the drawings: Figures 1 and 2 (already described previously) are, respectively, a plan view and a view according to the line H-Il of Figure 1 of a machine or work centre according to the state of the art;

Figure 3 is a plan view of a machine tool or work center according to the invention; Figure 4 is a view according to the line IV-IV of Figure 3;

Figure 5 is a front view according to the line V-V of Figure 3; Figure 6 is a plan view of an improved embodiment of a machine according to the invention;

¹ Figures 7 and 8 are, respectively, a plan view and a view according to the line VIII-VIII of a machine tool or work center with a particular type of loader or feed system; and

Figures 9 and 10 are, respectively, a plan view and a view according to the line X-X of Figure 9, of a machine tool or work center according to the invention with a different type of loader or system for feeding the pieces to be machined.

Detailed description of embodiments of the invention

With initial reference to Figures 3, 4 and 5, a first embodiment of the machine tool or work center according to the invention will be described.

In a way similar to what is described with reference to Figures 1 and 2, in the machine tool or work center of Figures 3, 4 and 5 a base or machine bed 101 is provided with guides 103 developing along the numeric-control axis X, in a direction horizontal and parallel to the longitudinal development of the base 101. On the guide 103 there translates an upright 105 of which MA designates the axis of vertical symmetry or the trace of the median plane.

Set on the upright 105 is an arm 107 with a substantially horizontal development, equipped with a second translation guide 109 extending along the longitudinal development of the arm itself.

Unlike what is envisaged in traditional machines, in the machine tool according to the invention the arm 107 is set with its own centroid B substantially on the median plane of trace MA of the upright 105 and hence substantially aligned to the centroid M of the upright 105 itself. Basically, then, the arm 107 is set symmetrically and projects in cantilever fashion from either side of the upright M, orthogonal to the numeric-control axis of translation X. Moving on the guide 109, in a controlled way along a numeric-control axis

Y, is a carriage 111 equipped in turn with a vertical guide 113. Translating along the guide 113 is a slide 114, which is mobile along a.third numeric- control axis Z. As in the machine or work center of Figures 1 and 2, the numeric-control axes X, Y and Z are hence substantially orthogonal to one another.

In the above example of embodiment, the slide 114 carries an operating or machining head 115 with a double chuck 117 equipped with coaxial tools U1 and U2. Designated by A and B are two numeric-control axes of oscillation or rotation orthogonal to one another, about which the chucks 117 can rotate or oscillate.

As may be noted in particular in the plan view of Figure 3, the guide 113, i.e., the pair of rails that constitutes said guide, are set on a substantially vertical plane inclined with respect to the numeric-control axis of translation Y. In Figure 3, the reference T designates the trace of said vertical plane. Consequently, the operating or machining head 115 is carried .by the carriage 111 in a position laterally staggered with respect to the median plane of the carriage 111 , on which the centroid "of the latter is located. Consequently, the chuck 117 can be carried into a position laterally staggered with respect to the axis X and to the base 101 by the same amount "a" by which the chuck 17 in the machine of Figures 1 and 2 can be translated laterally. However, unlike what occurs in the machine of Figures 1 and 2, this position can be reached with a much smaller length of the arm 107 and, more in particular, with an arrangement of this arm symmetrical with respect to the axis or median plane of trace MA of the upright 105.

It follows that the moments of inertia of the arm 107 and of the carriage

111 are much smaller in this case than in the configuration of Figures 1 and 2. The cantilever portions of the arm 107 are smaller, and consequently the bending that this arm undergoes during the accelerations of the upright 105 along the axis X is smaller. The mass of the arm 107 gives rise, in practice, to a very modest elastic deformation of the arm itself, since the centroid of the arm 107 is located on the median axis of trace MA. The static moment of the carriage 111 is also smaller than the static moment of the carriage 11 since the distance of the centroid of the carriage itself from the median plane MA of the upright 105 is smaller.

In practice, then, the accelerations along the axis X of the upright 105 cause undesirable displacements ηx of the tools U1 , U2 of the chuck 117, which are considerably smaller than the displacements that, all other conditions being equal, occur in machines having a traditional configuration of the type shown in Figures 1 and 2.

By reducing the cantilever portions of the arm 107, it is also possible to reduce the mass of the latter, in so far as it is possible to obtain equivalent stiffnesses with smaller masses. This constitutes a further advantage in terms of elastic bending deformation of the portions of arm 107 projecting in cantilever fashion from the chuck 105 during the acceleration along the axis X. The configuration of Figures 3 and 4 enables, then, lighter structures, faster accelerations and larger strokes along the axis Y to be obtained, given the same displacements ηx allowed, or else reduction in the undesirable displacements ηx, other parameters being equal. The need to reduce the undesirable displacements ηx is the more felt, the larger the mass of the operating head 115, and hence, in particular, in the case of heads with five axes, i.e., birotary heads like the ones illustrated and heads with a number of chucks, for example four chucks arranged in a cross.

Figures 3 to 5 show with a dashed line a symmetrical arrangement of a second upright 105 with a respective structure constituted by an arm 107, a carriage 111 , a slide 114, and a head 115, with corresponding guides. This indicates that the machine can be equipped with a single upright or a double upright with a symmetrical configuration for simultaneous machining of a workpiece P.

Figure 6 shows an improved embodiment of the invention jn a plan view.

Numbers that are the same designate parts that are the same as or equivalent to the ones of the embodiment shown in Figures 3 to 5. In this case, the carriage 111 has a slider 116 that can be adjusted along substantially circular arched guides 112 developing in a horizontal plane. The slider 116 carries the guide 113, translating on which, along the numeric-control axis Z, is the slide

114 carrying the operating head 115 with the chuck 117 and the tools U1 and

U2.

'With an arrangement of this kind, it is possible to orient, in any position between the two end positions indicated respectively by a dashed line and a solid line in Figure 6, the slider 116, provided on which are the guides 113 for the slide 114. It may be understood how this arrangement enables machining of pieces P to be obtained, arranged on either side of the base 101 , as schematically shown in Figure 6, where the of workpiece positioning areas are designated by P and Pl The displacement along the arched guide 112 of the slider 116 can be a numerically controlled displacement. On the other hand, this is not necessary, in so far as it is sufficient that the machine should be able to be brought into one or other of the two end positions indicated by a dashed line and a solid line in Figure 6 for machining, respectively, one or the other of the pieces set on the two sides of the base 101. It is therefore possible to adopt a simple system of translation along the guide 112 with limit switches for arresting the element of orientation of the slider 116, without any need for numeric control of this movement of oscillation.

The configuration of Figure 6 can also enable provision of a working area for the pieces in P and an area for tool change in P1 , so that the tool magazine and the means of tool change do not encumber the working area.

The machine tool or work center according to the invention can be equipped with various types of loaders or systems for feeding, supporting, clamping, and moving the pieces to be machined. There may, for example, be provided systems in themselves known for loading and unloading the pieces, which enable the pieces to be machined to be transferred from a loading position to the working position and the machined pieces from the working position to the unloading position. There may be provided, above all when the machine is equipped with a number of uprights, pendular systems for loading

pieces on a clamping table whilst a second piece clamping table is in the working position. An embodiment of this type is illustrated in Figures 7 and 8. A different configuration of the systems for loading the pieces is illustrated with reference to Figures 9 and 10. Also in this case, the loader is of a type known per se.

Indicated by a dashed line are perimetral protection walls for protecting the area where the tools carry out machining.

It is understood that the drawings show just one example, provided purely as a practical embodiment of the invention, which may vary in the forms and arrangements, without thereby departing from the scope of the idea underlying the invention. The possible presence of reference numbers in the attached claims merely has the purpose of facilitating reading thereof with reference to the description and to the drawings, and in no way limits the scope of the protection represented by said claims.