AUTOMATIC LATHE

Description

The present invention relates to devices for the guided feeding of bars towards an automatic lathe.

Automatic lathes, both of the single-spindle and multiple-spindle type, when they machine bars require a support device for the bar part which projects from the spindle on the opposite side to that where the bar is machined.

The bar, which is not necessarily circular, rotates together with the lathe spindle at speeds which may also be very high, for example up to 8000 to 10,000 rpm, and the support device must keep as far as possible the bar centred with the spindle axis, so that the bar and spindle are prevented from oscillating and the stresses generated by the rotating bar may be withstood. Moreover, the parts of the support device in contact with the bar must withstand the wear produced by the rotating bar. For example the rotating bar may be a bar with a very large hexagonal cross-section which rotates at high speed between the elements supporting it.

In the simplest systems, where the lathe itself feeds the bar and the bar is loaded manually, the channel which receives the bar in the support device is generally formed by a simple metal tube which has, inserted inside it, a long helical "undulating" spring, i.e. which has constrictions at regular intervals along its longitudinal axis. These constrictions therefore form a channel with a diameter slightly bigger than that of the bar and guide the bar itself during machining.

This system has several drawbacks. For example, the bar may be loaded only at the rear (additional space behind the bar-holder tube is therefore needed). Moreover, a shaped bar with a non-circular cross-section may be damaged by the spring during rotation (for example the edges of a hexagonal bar may become rounded at some points) and in general high speeds of rotation may not be reached because the elasticity of the spring may easily generate resonance which results in vibrations which make it impossible to remain within the machining tolerances. Moreover, when there is a variation in the diameter of the bar to be machined, the guide spring must be replaced with another spring which has suitable dimensions.

Other devices are provided with a channel for the bar, composed of support groups which are distributed at intervals along the said channel. Each group is formed by two semi-cylindrical shells which are arranged facing each other so as to define between them a cylindrical passage with a diameter slightly greater than the diameter of the bar to be machined. The shells have a variable length depending on the manufacturer and may be made of plastic, with or without additional lubrication. The shells are generally mounted on a lateral displacement system which allows the channel to be opened and allows the introduction of the new bar on the channel side, by means of an automatic bar loading magazine for example.

This system allows the bar to be rotated at high speeds, but still has the drawback that the shells must be replaced when there is a variation in the cross-section of the bar, so as to adapt the channel to the bar. This results in additional costs and in particular a considerable amount of time needed to perform replacement, in particular in the case of multiple-spindle lathes, where there may be a relatively large number of channels (for example six or eight channels) and with a limited amount of access space for replacement.

In the more complex systems, where the device forms a loader which also performs feeding of the bar, inside the channel there is also a bar pusher, i.e. a motor-driven shaft which has at its front end a spring gripper which grips the tail end of the bar inside the channel and moves it along said channel. This gripper keeps the rear end of the bar in the centre of the channel and allows recovery, at the rear, of the bar section which remains at the end of machining.

Unless the bar pusher is also replaced when there is a variation in the cross-section of the bar, the loader channel must have however the diameter of the bar pusher, i.e. a diameter slightly greater than that of the largest bar which can be machined. As a result the smaller bars are very free to oscillate inside the channel and therefore easily give rise to damaging vibration.

In these systems with a bar pusher there is therefore the advantage that the bar may be guided at the rear by means of the bar pusher gripper, but there is the disadvantage that it is not possible to ensure optimum guiding of the smallest bars. Loading devices with elements which form a channel having the diameter of the bar to be machined and which open automatically upon arrival of the bar pusher to allow the passage thereof have been proposed. These devices, however, are very complex and have dimensions which make them difficult to use in the case of loaders for multiple-spindle lathes, where the channels are very close together.

EP0574882 describes a device where the channel is not composed of semi- cylindrical shells, but by pairs of sprockets arranged radially alongside each other on both sides of the channel so as to define with their radial surfaces a passage for the bar. The sprockets may be rotated axially and have a diameter which varies about the axis of rotation so that, by rotating them into predefined positions, they define between them a passage of different sizes for the bar. EP0574882 describes four possible diameters which can be used and a fifth position which forms a spacious passage between the sprockets for lateral loading of the bar.

As the bar pusher advances, suitable mechanisms rotate axially the sprockets in succession so as to allow the passage of the bar pusher.

The sprocket system according to EP0574882 has the drawback of having a very small bar guiding surface, equal to a small segment of each sprocket. Consequently, even with abundant lubrication, the shaped bars damage quickly the sprockets. Moreover, with only four possible diameters of the channel, not all the bars may be guided in an optimum manner.

The general object of the present invention is to provide a bar feeding device which is able to overcome the aforementioned problems of the prior art, allowing rapid and suitable variation of the width of the channel, and which is relatively simple and sufficiently strong and reliable. An object of the invention is also to provide a manufacturing method and shells for defining guide channels in bar feeder devices. In view of these objects the idea which has occurred is to provide, according to the invention, a device for feeding a bar to an automatic lathe, comprising a guide channel for containment and axial sliding of the bar, which is formed by a plurality of support groups distributed along an axis of the channel, each support group comprising a pair of shells facing each other with surfaces which define between them the guide channel with a through-opening for the bar, characterized in that the two shells of each pair are pivoted so as to be rotatable controllably about an adjustment axis which is transverse to the axis of the channel and directed along a direction where the shells of the pair face each other, and that said surfaces are shaped so that when the shells are rotated about this adjustment axis the width of the through-opening changes.

Still in view of these objects the idea which has occurred is to provide a method for manufacturing a guide channel in a bar feeding device for automatic lathes, comprising the step of producing pairs of shells with surfaces which when facing define between them a guide channel with a through-opening for a bar along a channel axis, the surfaces being shaped so as to vary the through-opening upon rotation of the shells about an adjustment axis which is transverse to the axis of the channel and which is directed along a direction where the shells of the pair face each other when installed in the device.

Finally the idea which has occurred is to provide shells for the definition of guide channels for devices for feeding a bar to an automatic lathe, characterized in that it comprises surfaces which when facing each other in pairs define between them a guide channel with a through-opening for a bar along an axis of the channel, the surfaces being shaped so as to vary the through-opening upon rotation of the shells about an adjustment axis which is transverse to the axis of the channel and directed along a direction where the shells of the pair face each other.

In order to illustrate more clearly the innovative principles of the present invention and its advantages compared to the prior art, examples of embodiment applying these principles will be described below with the aid of the accompanying drawings. In the drawings:

- Figure 1 shows a schematic view of a bar feeding device for an automatic lathe;

- Figure 2 shows a schematic partial and perspective view of a guide channel of the feeder device according to the invention;

- Figure 3 shows a partial and perspective schematic view of the guide channel shown in Figure 2, but in an open position;

- Figures 4 and 5 shows schematic views, respectively a front elevation view and a plan view, of a pair of jaws coupled together in a first operating position for forming a section of the guide channel of the feeder device according to the invention;

- Figures 6 and 7 show schematic views similar to those of Figures 4 and 5, bur with the jaws of the pair in a second operating position;

- Figure 8 shows a schematic perspective view of a possible embodiment of a jaw according to the invention;

- Figure 9, 10 and 1 1 show schematic views, respectively a perspective view, plan view and front elevation view, of a jaw of the guide channel of a feeder device according to the invention;

- Figures 12 and 13 show a partial and perspective schematic view, respectively in the exploded condition and assembled condition, of an embodiment of a mechanism for adjusting the jaws in a feeder device according to the invention;

- Figure 14 shows a partial, schematic, side elevation view of another mechanism for adjusting the jaws in a feeder device according to the invention.

With reference to the figures, Figure 1 shows in schematic form a feeder device in accordance with the invention.

This feeder device, denoted overall by 10, comprises at least one channel 1 1 for axially guiding a bar 12 along the axis 17 of the channel towards an automatic lathe 13. The device 10 may be for example of the type (generally known in the sector as inserter) in which the bar is moved by the lathe itself and freely slides inside the channel 11 or may be of the type (generally known in the sector as loader) inside which there is also one bar pusher 14, suitably driven by means of a drive 29 known per se (for example a motor-driven chain or other known system) so as to slide inside the channel 1 1 . The bar pusher is provided with a gripper 15 for gripping the tail end of the bar inside the channel and pushing it along the channel towards the spindle of the lathe in order to retract inside the channel the residual bar section at the end of machining.

The device 10 may be of the single-bar type for single-spindle lathes and therefore have only one channel 1 1 , or of the multiple-bar type for multiple-spindle lathes and therefore have a plurality of channels 1 1 parallel to each other, each with their own bar pusher and rotating together with the spindles of the lathe, as may be easily imagined by the person skilled in the art.

The feeder device 10 may also be provided with a suitable magazine (known per se and therefore not shown or further described) for sequential removal of the bars to be loaded into the channel(s) 1 1 and/or for discarding the bar section left inside the gripper at the end of machining.

Figure 2 shows in greater detail the channel 1 1 (or one of the channels, in the case of a multiple-bar feeding) of the device 10 according to the invention.

This channel 1 1 is substantially defined by a plurality of support groups 16 which are distributed at intervals along the axis of the channel so as to contain, guide and support slidably the bar. Each support group 16 is formed by a pair of shells 18 (in contact with each other or separated by a small amount of play) facing each with their surfaces so as to define between them the guide channel.

The shells 18 are each rotatable about an axis 20 transverse to the channel and directed in the direction where the shells of the pair face each other.

The facing surfaces 22 of the shells which define laterally the channel 1 1 are shaped so as to vary the through-opening of the channel when they are rotated about this adjustment axis 20. In this way, it is merely required to rotate the shells about the transverse axis 20 in order to adapt the channel to a bar with a particular diameter. Advantageously the shells are supported on a special frame structure 19 along the channel and may be made advantageously of a plastic material chosen so as to have a sufficient rigidity and suitable smoothness coefficient, as may be imagined by the person skilled in the art. The total number of pairs of shells will depend on the length of the channel, the extension of the shells and the distance which is to be maintained between the pairs.

The shells 18 of each pair are pivotably supported on the frame structure 19 so as to be able to rotate about the adjustment axis 20 which is transverse to the channel and extends along the direction where the shells of the pair face each other.

The rotation which varies the through-opening may be advantageously designed so as to be symmetrical and opposite between the two shells of each pair.

Preferably a suitable mechanism may be used to produce the rotational movements, for example in synchronism and in an opposite manner, of the two shells of each pair with a single command.

Advantageously, the rotation mechanism may be designed to perform in synchronism the rotation of all the pairs of shells, as will become clear from below, so as to speed up even further the adjustment of the device 10 when there is a variation in the diameter of the bar to be fed to the lathes.

Preferably, the pairs of shells may be arranged around the channel so that all the shells on one side of the channel are aligned with each other along the axis of the channel so as to form a half-channel and all the shells on the other side of the channel are aligned along the axis of the channel so as to form the other half channel. In particular, a half-channel may be advantageously a bottom half-channel (namely the bottom half of the channel) and the other channel may be advantageously a top half-channel (namely the top half of the channel).

Advantageously, the shells on the two sides of the channel may also be supported by the frame structure 19 so that they can be moved away from each other in order to open the channel and thus allow easy insertion of a bar inside the channel by means of a transverse movement of the said bar on one side of the channel. This lateral insertion movement may also be performed by means of the known automatic magazine, as mentioned above. In order to allow the shells to be moved away from each other, for example the frame structure 19 may be formed by a first structure part 19a which supports the shells on one side of the channel and a second structure part 19b which supports the shells on the other side of the channel, with one of the two parts 19a, 19b which is movable controllably with respect to the other part 19b, 19a. The movement may be for example a rotational and/or translational movement performed by a suitable automatic or manual mechanism, which is known per se and therefore may be easily imagined by the person skilled in the art.

For example, as shown also in Figure 3, a suitable mechanism 53 (for example of the cam type) may be provided and may be operated by a known actuator (not shown) so as to rotate the part 19a about an axis 21 parallel to the axis 17 of the said channel. Advantageously, the shells which rotate about the axis 21 may be the shells which form a top half-channel, so that the shells on the other side of the channel (namely the shells on the bottom side) form a cradle for receiving the bar to be fed which is deposited on them when the channel is open.

Figures 4 and 6 show two possible shells of a pair according to the principles of the present invention. As can be seen in these figures, the two shells form with their facing surfaces 22 a through-opening 25 through which the bar slides inside the channel.

As already indicated above, the surfaces 22 of the shells are shaped with a progression such that transverse dimension of the through-opening 25 between the two shells 18 of each pair varies depending on the angle of rotation of the shells of the pair about the adjustment axis 20.

In particular, the surface 22 may be shaped such that the through-opening along the axis 17 of the channel varies from a maximum diameter (as can be seen for example in Figure 4) to a minimum diameter (as can be seen for example in Figure 6) when there is a variation in the symmetrical and opposite rotation of the shells about the common adjustment axis 20.

Advantageously, the surface 22 may be shaped such that the switch-over between the maximum dimension and minimum dimension of the through-opening coincides with the rotation of the shells about the adjustment axis 20 from a position where the main axis 58 of the shells (or also maximum passage axis) is arranged substantially parallel to the axis 17 of the channel (Figure 5) to a position of the shells where the axis 58 has a maximum angle with respect to the axis 17 of the channel (Figure 7).

As can be seen also in Figure 7, the rotation of the shells may be advantageously opposite and symmetrical with respect to the axis 17 of the channel. The two shells of the pair may be advantageously made substantially identical to each other, and likewise their surfaces 22 may be made substantially identical.

Advantageously, the progression of the surfaces 22 may be preferably chosen so that the through-opening 25 remains substantially circular, while varying its diameter when the shells are rotated about the adjustment axis 20. In this way, the bars fed along the channel are contained laterally inside the channel in a substantially uniform manner in all the radial directions.

In an advantageous embodiment, the surface 22 may be shaped so that it forms (at least over its part 24) the envelope of a plurality of cylinders with a decreasing diameter, arranged with axes which are coplanar with a same plane (preferably perpendicular to the adjustment axis 20) which also contains the axis of the channel and angularly rotated with increasing angles about the adjustment axis 20 as the diameter decreases. This is shown schematically in Figure 8 which shows a cylinder with a maximum diameter (in broken lines) and a cylinder with a minimum diameter (in solid lines) and which represent the ends of the envelope of the desired part of the surface 22. The cylinders shown in Figure 8 may also be regarded as representing bars which can be received in the two positions (less a small amount of lateral play). The number of angular positions may be separated or continuous. In particular, the rotation of the shells may be adjustable stepwise, with each step adapted to a bar diameter (or a range of bar diameters between a maximum and a minimum for that angular position) or may be continuously adjustable.

The desired surfaces 24 may be formed (or shaped as though they were formed) by performing a sequence of suitable milling operations on the shell along a fixed axis (which will then correspond to the axis of the channel of the feeder device), while the shell is suitably rotated about its axis 20.

The milled zones may be real milled surfaces, namely formed on the shell being produced, or may be virtually reproduced in a CAD program, used for the design drawing of the shells, so as to define the surface 24 which is then subsequently formed in the shell. In any case, the surface may be produced by directly machining a rough-made shell, by means of stock removal (for example using a numerical control milling machine) or may be first reproduced in negative form as a surface of a suitable mould for production of the shells by mean of moulding.

The rotation axis 20 may be in the centre of the two ends of the channel segment defined by the surface 22 of the shell.

In order to clarify further the advantageous form which the surface defining the channel in a shell according to the invention may have, an example of embodiment of such a surface is described hereinbelow with reference to Figures 8 to 1 1 . Let us consider for example a shell 18 (for example 150 mm long) and imagine that the surfaces 24 still do not exist and that there exists (or has been formed) only one semi-cylindrical groove 23 with an axis advantageously coinciding with the axis 58 and with a predefined diameter (for example 25 mm) suitable for the maximum bar diameter which is to be accommodated inside the channel of the device 10.

Let us now take as a reference position a "zero" axis (which will then coincide with the axis of the bar feeding channel inside the device 10) at the moment coinciding with the axis of the semi-cylindrical channel.

Let us then imagine rotating through a certain angle (for example 5 degrees in an anti-clockwise direction) the shell 18 about its central axis 20 and performing a milling operation using a half-round milling cutter (for example with a diameter of 22 mm) still along the "zero" axis (which is no longer the axis of the semi-cylindrical channel 23, but will be rotated through 5 degrees with respect to this axis). In this way a semi circular groove with a diameter of 22 mm is obtained on the shell, said groove being aligned with the zero axis and intersecting the initial semi-cylindrical groove 23.

Let us now imagine rotating the shell another 5 degrees and performing a third milling operation using a half-round milling cutter with an even smaller diameter, for example 19 mm, along the zero axis, and so on, increasing each time the rotation by 5 degrees and decreasing the diameter of the milling cutter (for example with the sequence of diameters of 16 mm, 13 mm, 10 mm and 7 mm). The complex surfaces 24 are thus obtained.

If the axis of rotation 20 is in the centre of the shell, as shown in the figure, the complex surfaces 24 are two in number on opposite sides and at opposite ends of the initial groove 23, as shown by way of example in the figures.

By arranging the two shells thus obtained opposite each other it is clear, with each 5 degrees rotation of the shells, in the opposite sense, viewing the bar sliding channel in cross-section, a through-opening which is round, but has an increasingly smaller diameter equal to the mills used (in the example 0 25 mm, 22 mm, 19 mm, 16 mm, 13 mm, 10 mm and 7 mm) is obtained.

By aligning a plurality of pairs of shells to form the guide channel, the bar through- hole, viewed in cross-section, may be made bigger or smaller by simply suitably rotating the pairs of shells as desired.

It should be noted that, owing to the present invention, for each selected diameter, the support for the corresponding bar is very considerable in the longitudinal direction and each shell ensures a relatively large contact area with the bar in each configuration.

It is also now clear that by increasing the number of angular intervals into which the total rotation of the shell is subdivided and by increasing therefore the number of corresponding "milled zones" with a gradually decreasing diameter (with increasingly smaller intervals between successive diameters), twenty four increasingly smoother surfaces will be obtained, until a completely smooth surface is formed, this being equivalent to an interpolating curve tangential to all the infinite cylinders with which the shell may be imagined as being milled, between the minimum and the maximum bar diameter which is to be machined in the device. A curve of this type may be easily obtained using CAD-CAM machines also only by only mathematically interpolating a suitable finite number of decreasing cylinders, as may now be easily imagined by the person skilled in the art.

Figures 9, 10 and 1 1 show in greater detail a possible form of a shell 18 according to the principles of the present invention.

Preferably, as can be clearly seen in Figures 9, 10 and 1 1 , the surface 22 of each shell is formed with the semi-cylindrical groove 23 having a diameter equal to the maximum diameter of the bar which can be accommodated in the channel, and two complex surfaces 24 on opposite sides of the groove 23 which form the symmetrical contact surfaces for a bar with a diameter which gradually decreases as the two shells rotate about the axis 20 towards the smallest opening condition 25.

Each shell 18 may also have front and rear attack surfaces 26 which are inclined so as to form an inlet for the front end of the bar during its sliding movement along the channel.

On the sides of the recess formed with the shaped recess 22 which receives the bar, each shell of a pair may be formed with a flat surface 27 which is perpendicular to the axis 20 and which may be mated with the flat surface 27 of the other shell of the pair so as to allow the rotation of the shells around the axis 20 without impediment and (if in contact with each other) with minimum friction.

Each shell may also have some lateral chamfers 28 designed to reduce the dimensions thereof in some working positions (in particular when the two shells of the pair reach the maximum relative inclination), as is clear also from the comparison of Figures 5 and 7.

As can be clearly seen in Figure 12, the structure 19 supporting the shells may comprise a support plate 30 which extends along the axis of the channel and on which each shell 18 on the corresponding side of the channel is pivotably mounted along its axis 20. The rotatable pivoting of each shell may be performed by means of a screw 31 passing through a passage 33 in the shell and a hole 34 in the support plate 30 and then fixed using nuts 32 on the opposite side of the plate 30.

The pairs of shells which define the channel according to the invention could be rotated manually one by one about the axis 20 and then locked so as to determine a desired width of the guide channel depending on the bars to be fed. Already in this way, there could be an advantage in terms of the speed of adapting the feeder device 10 to a new bar diameter, instead of changing all the shells as is instead required according to the aforementioned solutions of the prior art.

Preferably, owing to the innovative principles of the present invention, it is however also easy to connect kinematically the shells for controlled rotation thereof, by means of a mechanism 35 for performing controlled rotation about the adjustment axis 20. The mechanism may also produce synchronous rotation of a certain number or of all the shells on one side of the channel, so as to perform adaptation of the channel even more rapidly.

Various mechanisms for rotation about the axis 20 may be used. For example, it is possible to use crank-and-rod mechanisms, with tie-rods, chains and pinions, gearwheels, etc., which are moved manually or are driven and which impart a rotational torque to the shells about the axis 20.

Figures 12 and 13 show for example a possible mechanism which provides a such a kinematic connection.

These figures clearly show the mechanism for rotating the shells 18 on one side of the channel (preferably the bottom side). On the other side of the channel the mechanism for adjusting the direction of the shells may be substantially the same. The two mechanisms may also be suitably connected together so as to operate in synchronism and rotate oppositely in synchronism the shells of the pairs concerned. As shown in the figures, a mechanism for rotating the shells about the axes 20 may advantageously comprise an adjustment plate 35 extending along the channel and kinematically connected to the shells so as to cause rotation thereof about the axes 20 when the said plate is rotated parallel to the axis of the channel.

The adjustment plate 35 may be advantageously packed with a small amount of play between the support plate 30 and the shells pivotably mounted on the plate 30 so as to be slidable with respect to the support plate 30.

The adjustment plate 35 is advantageously constrained to slide on the plate 30 in a direction longitudinally for example by means of straight slots 36 through which the screws 31 pass and which also act as a guide for sliding of the plate.

The kinematic connection between the adjustment plate 35 and the shells for causing rotation of the shells may be of various types, for example of the rack type, crank- and-rod type, etc.

One kinematic connection which has been found to be advantageous comprises for example slots 37 and 38 formed in the adjustment plate 35 for each shell to be rotated. These slots are arranged suitably spaced from the axis of rotation 20 and two pins 39, 40 which project from the rear pivoting side of each shell (namely the side opposite to the side with the surface 22) engage inside said slots.

The slots 37, 38 have a circular shape so that the longitudinal sliding of the plate 35 on the plate 30 corresponds to a proportional rotation of each shell 18 about the respective axis 20, owing to the cam action of the pins 39, 40 inside the curved slots 37, 38.

In this way, it is merely required to slide the plate 35 in order to adjust suitably all the shells connected to it and obtain the desired through-opening for the bar.

Displacement of the plate 35 may be obtained with various adjustment systems which are substantially known per se.

For example, in the figures the plate 35 is connected to a manual control device 41 which, by means of a manual adjustment element 45, allows adjustment of the position of the plate 35 and consequently the rotation of the shells connected thereto. By means of said control device 41 it is possible to perform a fine adjustment of the longitudinal position of the plate 35 in a simple and rapid manner so as to obtain a predetermined size of the through-opening in the channel.

The control device 41 comprises a slider 42 which is constrained to move inside two perpendicular slots 43, 44 formed respectively in the support plate 30 and in the adjustment plate 35. Sliding of the slider 42 along the slot 44 thus produces a corresponding sliding movement of the adjustment plate 35 with respect to the support plate 30. The sliding movement may be for example controlled by an adjustment screw 45 which is screwed into the slider 42 and which has its head constrained inside a seat 46 so as to rotate, but not slide inside a block 47 which is in turn constrained to the support plate 30.

Rotation of the adjustment screw 45 thus moves the slider 42 and forces the plate 35 to follow the movement of the slider. The position of the plate 35 with respect to the support plate 30 may be advantageously visibly displayed with precision on a graduated scale 48 which is fixed to the block 47 and along which a pointer 49 fixed to the adjustment plate 35 slides.

Advantageously, the corresponding diameters which are created along the channel for the various positions of the slider may be indicated directly on the graduated scale 48.

Preferably, a further fixing screw 50 passes through a slot 59 in the plate 35 and is screwed into the plate 30 so as to allow relative locking in position of the adjustment plate 35 with respect to the support plate 30 and therefore fixing of the angular position of all the shells 18 once the adjustment has been performed.

Since it is advantageous also for the shells on the other side of the guide to move in synchronism, the rotation mechanism on one side of the channel may be connected to the rotation mechanism on the other side and a single adjustment system which thus operates in synchronism both the rotation mechanisms may be provided.

In particular, in the case of the rotation mechanism described above with reference to Figures 12 and 13, the shells on the other side of the channel may have a mechanism similar to that described above with its own adjustment plate 35 kinematically connected to the plate 35 of the first mechanism so as to obtain an opposite and mirror-image movement of the two shells of each pair with respect to the axis of the channel.

For example, Figure 3 shows by way of example how it is possible to connect the two adjustment plates 35 so that moving one plate moves also the other plate. In particular, a bracket 51 may be advantageously provided, said bracket being rigidly constrained to one of the two adjustment plates and engaging inside a corresponding slit 52 in a connector 54 rigidly connected to the other adjustment plate.

Advantageously, the bracket 51 engages inside the slit 52 slidably in a direction transverse to the channel so as to allow opening of the two half-guides and the lateral introduction into the channel of a bar to be fed to the lathe, while keeping in any case the positions of the two adjustment plates synchronized also when the half guides are open.

Obviously, if the adjustment mechanisms are interconnected, it is sufficient to have a single control device 41 on one of the two mechanisms. For example, the control device may be mounted on the bottom mechanism which in the embodiment shown remains stationary during opening of the guide.

In the case where the principles of the present invention are adopted in order to realize loading devices with a bar pusher, it is sufficient to provide a lateral recessed zone between each pair of shells (as shown schematically in broken lines and indicated by 57 in Figure 4) in order to allow the insertion of a connecting plate between the bar pusher and the drive which moves it and which is usually situated laterally on the outside of the channel, as can be seen for example in Figure 1.

If the bar pusher is used, it is also easy to provide a system for the selective control of rotation of the shells which operates the various pairs of shells so as to allow the rotation of each pair of shells in sequence towards the maximum through-opening position when the bar pusher arrives. This therefore achieves the aim of suitably guiding a bar by means of a channel with a suitable adjustable diameter, while allowing the bar pusher to pass through when necessary.

Figure 14 shows in schematic form a possible system for such a selective command. In this system an adjustment mechanism 55 is used for each shell (or pair of shells). This adjustment mechanism 55 comprises a mechanical sensor 56 which is arranged upstream of each pair of shells and which detects the arrival of the gripper 15 of the bar pusher, which has a diameter greater than that of the bar. The movement produced by the sensor 56 performs the rotation of the shells 18 of the pair towards the fully open position of the through-opening. This can be seen from Figure 14. The mechanism for rotation of a shell (or the pair of shells) may be per se similar to that described above for all of the shells.

During the return movement of the bar pusher the sensors 56 may bring the shells back into their set position for the specific bar to be fed along the channel.

The sensor 56 and the control system may also be electromechanical, with an electric switch which is operated by the passing movement of the gripper and which operates an electromechanical actuator which rotates the pair of shells, as may now be easily imagined by the person skilled in the art.

Moreover, it is also possible to use a sensor 56 and an adjustment mechanism 55 for more than one pair of shells in sequence, if for example it is not required for the tail end of the bar to be guided with a set through-opening for its diameter also in the vicinity of the gripper. For example, the two, three or more pairs of shells immediately in front of the gripper could be opened together such as to simplify further the mechanism.

At this point it is clear how the objects of the invention have been achieved.

From the above description it is clear how with a device according to the invention it is possible to perform rapid and precise variation of the channel diameter so as to hold a bar with a small amount of lateral play, while also maintaining a relatively large contact surface between the bar and the channel, without the need to remove and/or replace channel sections.

By rotating through a suitable angle the shells 18 about their axis 20 it is possible to obtain in a simple and reliable manner a variable diameter channel which is suitable for the various bar diameters, for example for receiving with a minimum amount of play a bar inside the channel.

Unlike the prior art, the bars are laterally guided inside the channel by means of surfaces which are relatively large and therefore less subject to wear. It is thus possible to guide in a satisfactory manner also bars which have a non-circular cross- section with edges.

Moreover, in the advantageous embodiment described for the surfaces defining the channel with reference to Figures 8-1 1 , each pair of shells defines two relatively large surfaces for supporting the bar which are spaced from each other at the ends of the pair in the axial direction of the channel and this has been found to be particularly advantageous for reducing the wear of the shells and the vibrations of the rapidly rotating bar.

As can be understood for example from Figure 8, the axis of a bar with a smaller diameter than the maximum diameter is inclined with respect to the axis of the maximum groove 23 and the bar is guided by two opposite portions of the complex surfaces 24. The presence of the other shell of the pair (not shown in the figure) ensures gripping of the bar on two further symmetrical and oppositely arranged complex surfaces 24. The bar is therefore guided by each pair of shells in four long thin zones situated opposite each other in pairs. Each pair of shells therefore guides the bar inside four thin zones in a cross arrangement, containing and limiting any possible oscillation outside of the axis.

Owing to the configuration of the guide surfaces inside the shells, situated at the front and rear ends of the shells, moreover, it is easy, where required, to provide a spray lubrification system which may help further dampen vibrations and noise and protect the shells from wear due to the contact with the rotating bar.

The mechanism for adjusting the through-opening may also be simple and small in size.

Since the system has a small size in each radial direction compared to the maximum channel diameter which is created, multiple-bar feeding devices for multiple-spindle lathes may be easily provided. In this case it is also possible to install easily connections between the various guide plates, so as to centralize adjustment of the diameter of all the channels, as may now be easily understood by the person skilled in the art. In addition to being low-cost, the system is therefore also suitable for providing multiple-bar feeder devices with a relatively large number of parallel channels and/or with a small transverse space between the channels.

Obviously the description given above of embodiments applying the innovative principles of the present invention is provided by way of example of these innovative principles and must therefore not be regarded as limiting the scope of the rights claimed herein.

For example, the mechanisms for adjusting, rotating and displacing the pairs of shells may be varied also depending on the specific practical requirements, these being able to be designed with different mechanisms and/or different control systems of the chain or crank-and-rod type, or gear drives, of the manual, electromechanical or pneumatic type.

The feeder device may also comprise further known mechanisms associated with this type of device, such as mechanisms for synchronizing operation thereof with the lathe for feeding the bars inside and outside of the channel, for the controlled movement of the pusher, etc.