In particular the rotary table of the present invention can be used in centres for machining workpieces, commonly called work centres.

A work centre comprises, in its simplest version, a tool-holder chuck for machining workpieces and a support surface on which the workpiece to be machined is clamped, these being fixed or displaceable along one or more working axes such as those defined by the mutually perpendicular Cartesian planes X, Y, Z. Figure 16 shows, for example, a work centre with three axes, where the surface supporting the workpiece is movable along the axis Z, corresponding to the axis of the chuck, and the chuck is mounted on a support movable along two axes X and Y perpendicular to each other. Depending on whether the axis of the chuck is arranged in the horizontal direction or vertical direction, the term"horizontal work centres"or"vertical work centres"is used respectively.

Work centres of the type mentioned above are known in the art of the sector and are used to perform a plurality of milling, boring, tapping or other operations on parts to be machined.

Should it be necessary to rotate the workpiece with

respect to the machining tool, the work centre is equipped with a rotary table having a workpiece holder plate able to rotate about an axis of rotation B (Fig.

16).

Work centres of the type described above are defined as being of the four-axis type and allow machining operations to be carried out, with single gripping of the workpiece, on the surfaces of the workpiece situated about the axis of rotation B and parallel thereto.

In the case of horizontal work centres, the axis of rotation B of the table is arranged vertically, while, in vertical work centres, the axis of rotation B of the table is arranged horizontally.

The rotary table may be of the"continuous"or"indexed" type in the case where fixed orientation of the workpiece with respect to the tool-holder chuck is sufficient. Normally, in horizontal work centres, the table is already incorporated in the support surface of the machine, whereas in vertical centres, it is mounted above the support surface.

Should it be required to perform the machining of the side of the workpiece which is not normally accessible by the chuck and/or in different inclinations, it is required to use five-axis work centres equipped with rotary tables mounted on a tilting cradle able to provide an axis of rotation C in addition to the axis of rotation B provided by the table and arranged perpendicularly with respect thereto.

On work centres of the type described above it is possible to perform, again with single gripping of the workpiece, for example inclined milling or boring operations.

It is necessary to emphasise, however, that the installation of a rotary and tilting table in a work centre affects the design and the architecture of the work centre, namely the machine, on which the table is to be installed, both from a mechanical point of view and from the point of view of the control system managing the work centre, with a consequent increase in the final cost of the work centre itself.

Consequently the work centres equipped with rotary and tilting tables, namely five-axis work centres, although allowing the execution of a plurality of machining operations, have considerable drawbacks in terms of costs of the work centre.

These drawbacks are particularly evident if one considers the fact that the use of the fifth axis is restricted to extremely complex machining operations, while most machining operations may be performed using the work centre as a four-axis machine.

In recent years, the need to optimise the machining time and cost has resulted in the introduction of work centres equipped with pallet-changing systems. In the case in question, the workpiece is fixed to a pallet able to be associated with the rotary and/or tilting table of the work centre. In this way, once the part has been machined, the pallet may be removed automatically

from the work centre and therefore is ready to receive another pallet with a new workpiece.

It is clear that the work centres with four or five axes and with a pallet-changing system must be manufactured with tables already equipped with pallet fixing devices and have a series of fixed electrical, hydraulic, pneumatic or other connections with the said table.

This results in not insignificant costs both as regards the mechanical design of the work centre and the complexity of the numerical control programs, with a consequent increase in the final cost of the work centre.

Consequently, in order to carry out more complex machining where a fifth machining axis is required, it has been proposed to use a pallet which can be loaded onto and unloaded from the work centre and is equipped with a rotary table able to rotate about a second axis of rotation in addition to the vertical axis provided by the work centre.

An example of a pallet equipped with a rotary table is illustrated in the document JP-1051251-A.

According to the known art indicated above, a pallet fixed to a table of a work centre, rotatable with respect to its vertical axis, is equipped with a workpiece holder cube provided with a rotary table having a pair of support devices on which the workpiece is clamped. The support devices, or workpiece holder plates, are designed to be actuated rotationally about the horizontal axis of the workpiece holder turret, thus

allowing the rotation of the workpiece about an axis of rotation in addition to the vertical axis provided by the work centre.

The rotational actuation of the workpiece holder plates is performed by means of hydraulic actuating mechanisms.

In particular, the rotary table is provided with a hydraulic motor able to cause rotation of a gearwheel with a worm operationally associated, by means of a rotational shaft, with each workpiece holder plate.

In a similar manner, the mechanism for locking/releasing the workpiece holder plate is of the hydraulic type. In the specific case in question, the rotary table has a piston which slides inside a cylinder chamber and can be actuated by means of a hydraulic fluid.

Owing to the large amount of power required to rotate and lock the workpiece holder plates, the power must be supplied by an hydraulic control unit of suitable size.

For this purpose the table of the work centre is provided with a series of hydraulic coupling devices which, by means of the pallet, allow the connection of a hydraulic power unit arranged for example in the vicinity of the work centre, with the mechanisms for hydraulically actuating the rotary table mounted thereon.

The need to provide hydraulic connections between the rotary table and the work centre obviously limits the application of the pallet with table to only those work centres provided with suitable means able to allow

insertion or interruption of the connections when the pallet is respectively loaded onto or unloaded from the machine.

From this it can be deduced that the solution proposed in the document JP-1051251-A is applicable only to work centres which are suitably customized, whereas it cannot be used in work centres of standard design and therefore without the means for performing the connections between the work centre and the rotary table mounted on the pallet.

Consequently there is a strong need to provide of rotary tables, for equipping a pallet for work centres, which can be easily installed in standard work centres, only when required and without the need for hydraulic, electrical or pneumatic connections with the said centre.

The object of the present invention is that of providing a rotary table having structural and functional characteristics such as to satisfy the abovementioned requirements and avoid at the same time the drawbacks mentioned above with reference to the known art.

This object is achieved by a rotary table for work centres in accordance with Claim 1.

Another object of the invention is that of providing a rotary table which, when supported by a pallet for work centres, allows the introduction, within the work centre in which it used, of an axis of rotation in addition to that already available.

Further characteristic features and advantages of the rotary table according to the present invention will emerge from the following description provided below of a preferred non-limiting example of embodiment thereof, with reference to the accompanying figures in which: Figure 1 is a schematic perspective view of a rotary table according to the invention; - Figure 2 shows a different, schematic, perspective view of the rotary table according to Figure 1; Figures 3 and 4 show different schematic, perspective, views of the rotary table according to Figure 1, in the operative configuration; - Figure 5 shows an exploded view of the rotary table according to Figure 3; - Figure 6 shows an application of the rotary table according to Figure 3; Figures 7 and 8 show perspective views of the rotary table according to Figure 3 in non-operative configurations; Figures 9 and 10 show different, schematic, perspective views of a second embodiment of the rotary table in accordance with the invention; Figures 11 and 12 show different, schematic, perspective views of the rotary table according to

Figure 9 in the operative configuration; Figure 13 shows an exploded view of the rotary table according to Figure 9; Figure 14 shows a schematic planar view of the rotary table according to Figure 9; Figure 15 shows a sectioned planar view of a detail of the rotary table according to Figures 1 and 9; and Figure 16 shows a three-axis work centre.

With reference to the accompanying figures, 1 denotes overall a rotary table 1 in accordance with the present invention.

The rotary table 1 comprises a base body 2 and a workpiece holder plate 4 rotatable with respect to the base body 2 about an axis of rotation indicated by X-X.

The rotary table 1 of the present invention is of the indexed type with N positions, namely allows the workpiece holder plate 4 to be rotationally actuated between a finite number N of positions, for example 360.

In accordance with a preferred embodiment and as shown in the accompanying figures, the base body 2 is fixed to a support structure 3 provided with a plate 3a for fixing the rotary table 1 to a conventional pallet 20.

In order to actuate rotationally the workpiece holder

plate 4 about the axis of rotation X-X, the rotatable table 1 according to the invention is provided with operating means 5.

The operating means 5 are electric motor means, for example a brushless servomotor. The use of a servomotor is particularly advantageous when it is provided with an operating system incorporated inside the said motor as described for example in European patent application EP-A-768,585.

In order to supply the operating means 5, the rotatable table 1 is provided advantageously with power supply means 12.

In accordance with a preferred embodiment, the power supply means 12 comprise a battery power supply unit consisting of a housing 13 designed to receive one or more batteries 14. Advantageously the batteries 14 of the power supply unit 12 are of the rechargeable type and may be recharged directly when still inside the housing 13 or may be removed and recharged separately.

In the first case (Fig. 7), it is necessary to equip the rotary table 1 with electrical connection means 21 connected to the batteries 14 of the power supply unit 12 and able to be supplied, when necessary, by an external battery charging unit 22. The battery charging unit 22 may be supplied, for example, by a mains power supply or by a power supply provided by the work centre.

In the second case (Fig. 8), the housing 13 comprising the batteries 14 may be removed from the table 1 and replaced with a new power supply unit 12.

The electric motor 5 is a motor able to operate at low voltages, for example 24 volts, as supplied by the batteries 14, and 200 W of power.

In order to supply a voltage sufficient for supplying the electric motor 5, it is possible to use several batteries in series so as to generate the required voltage of 24 V.

For example, it is possible to use two 12 V batteries in series, each able to supply a current of 12 A/h for a total of 24 A/h, or four 12 V batteries, paired in series and supplying 38 A/h, for a total of 76 A/h.

The electric motor 5 is operated only for the time necessary to allow the angular rotation of the workpiece holder plate 4 into the desired position. For example, it is sufficient to operate the motor for 0.5 seconds in order for the workpiece holder plate 4 to be rotated into the desired angular position.

The rotary table 1 according to the invention also comprises locking means 6 for locking and releasing the workpiece holder plate 4 relative to the base body 2.

In accordance with a preferred embodiment, the locking means 6 are housed in the base body 2 and may be formed, for example, by means of a series of suitably shaped crown gears connected to the workpiece holder plate 4.

Alternatively the locking means 6 may be formed with different structures, for example by means of coupling elements of the multiple-disk brake type.

The locking means 6 must be suitably actuated so as to produce locking and release of the workpiece holder plate 4. For this purpose, the rotary table 1 comprises actuator means 7 for actuating the locking means 6.

Advantageously, the actuator means 7 act on the locking means 6 so as to allow unlocking of the workpiece holder plate 4 with respect to the base body 2, while locking of the locking means 6 is obtained by means of a mechanical device including preloaded springs, as described for example in the European patent application EP-A-782,901. Alternatively, the actuator means 7 may perform both locking and unlocking of the locking means 6.

In order to actuate the actuator means 7 of the locking means 6, the rotary table 1 comprises an energy source 10 mounted on-board the rotary table 1. In accordance with a preferred embodiment, the energy source 10 is a fluid-dynamic energy source which comprises a fluid- dynamic motor 10a suitable for actuating the actuator means 7 and an electric motor 10b for actuating the fluid-dynamic motor 10a.

The electric power supply of the electric motor 10b of the fluid-dynamic energy source 10 is advantageously supplied by the power supply unit 12. Preferably, the fluid-dynamic energy source 10 is of the hydraulic type.

In this case the fluid-dynamic motor 10a takes the form of a hydraulic pump 10a in fluid communication with a tank 9 for storing hydraulic liquid, also mounted on- board the rotary table 1.

Advantageously, the fluid-dynamic energy source 10 comprises a pressure accumulator 24 able to provide the instantaneous flow of fluid necessary for rapid release of the unlocking means 6.

The electric-motor 10b is of the type with a low power consumption, in the example has a power of 150 W, since it is operative only for a few brief moments, for example a few seconds, generally less than 10 seconds, necessary for restoring the nominal pressure of the accumulator 24. Preferably, the motor 10b is activated when the motor 5 is not active.

The fluid-dynamic energy source 10 preferably comprises a pressure sensor 11 for detecting the pressure of the pressure accumulator 24.

Alternatively, the fluid-dynamic energy source 10 is of the pneumatic type as described, for example, in United States patent US-5,787, 767 and in European patent application EP-A-782,901. In this case the fluid-dynamic motor 10a is in the form of a pneumatic compressor 10a.

Obviously, the fluid-dynamic energy source 10 for actuating the actuator means 7 may be realized by means of other hydraulic or pneumatic structures.

For example, the fluid-dynamic energy source 10 may comprise a tank 9 of the replaceable type, containing fluid under pressure. When the pressure of the fluid contained in the tank 9 falls below a value sufficient for actuating the actuator means 7, the tank 9 may be

replaced with another one load.

The use of this embodiment is advantageous since it avoids mounting on-board the table 1 the fluid-dynamic motor 10a and the electric motor 10b.

In the case of a hydraulic energy source, a tank 9 for hydraulic liquid or an accumulator 24 mounted on-board the table 1 will be available, while in the case of a pneumatic energy source, a pressurised air tank 9 will be used.

According to an alternative embodiment not shown in the figures, the energy source 10 is an electric power source which comprises an electric motor suitable for actuating the actuator means 7. The electric motor may for example rotationally actuate a cam shaft operationally associated with the actuator means 7. In this case, the electric motor has a very low power consumption, since it is operative only for very short time periods, for example about one second, necessary for releasing the locking means 6. Preferably the electric motor is activated when the motor 5 is not active.

Alternatively, the energy source 10 is an electromagnetic energy source, for example an electromagnet, able to actuate the actuator means 7. In this case also, the power consumption is extremely small as for the case described above.

Control of the operating means 5 and the energy source 10 is performed by control means 15 mounted,. on-

board the table and advantageously supplied by the power supply means 12.

In accordance with a preferred embodiment, the control means 15 comprise an electronic control apparatus (not shown in the figures) housed in a box 16 accessible from the outside for any repairs, replacement operations or updating of the control electronics of the rotary table 1. The control means 15 are connected to the electric motor 5, so as to control rotational actuation of the workpiece holder plate 4, and to the energy source 10, so as to control actuation of the actuator means 7 and therefore locking/release of the locking means 6 of the workpiece holder plate 4.

For this purpose the control means 15 are connected, in the case of a fluid-dynamic energy source, to the electric motor 10b and to an electric valve 23 by means of which the fluid for actuating the actuator means 7 is controlled.

In the case where only the replaceable tank 9 is present, the control means 15 cause actuation of the electric valve 23 so as to control the fluid leaving the said tank 9.

Again, in the case of an electric or electromagnetic energy source, the control means 15 respectively actuate an electric motor or an electromagnet.

The rotary table 1 also comprises communication means 17 able to exchange signals with corresponding communication means 17'of the work centre and with the

control means 15 of the rotary table 1. In this way the communication means 17 establish communication between the rotary table 1, or the control means 15, and the work centre. Exchanging of signals between the communication means 17 of the rotary table 1 and the communication means 17'of the work centre is performed advantageously in a wireless manner.

In accordance with a preferred embodiment, the communication means 17 and 17'comprise respective electromagnetic-wave transceiver devices. The transceiver device 17 is installed on the rotary table 1, while the transceiver device 17'is installed on the work centre.

In accordance with a preferred embodiment, the electromagnetic waves for communication between the rotary table 1 and the work centre are radio frequency waves. Alternatively, the electromagnetic waves are optical frequency waves. In this case the transceiver devices 17 and 17'are infrared or laser devices.

In order to be supplied, the transceiver device 17 of the rotary table 1 is in electrical communication to the control means 15 from which it receives the power supply. Alternatively, the transceiver device 17 may be supplied directly by the battery power supply unit 12.

The transceiver device 17'of the work centre is instead connected to a data conversion apparatus, for example a PLC, so as to be able to interface with the numerical control system of the work centre.

The rotary table 1 is advantageously provided with a casing unit 25 intended to protect the internal components of the rotary table.

The operating principle of the table 1 according to the present invention is described hereinbelow by way of example, in the case of a fluid-dynamic energy source 10 of the hydraulic type and starting from a situation where the table 1 is in rest condition. In this condition the batteries 14 must supply only the communication means 17. When a signal for positioning the workpiece holder plate 4 is transmitted by the communication means 17'of the work centre to the communication means 17 of the table 1, the control means 15 activate the hydraulic energy source 10.

Firstly the control means 15 enable operation of the electric motor 10b and opening of the electric valve 23 so as to actuate the actuator means in order to release the locking means 6. As soon as release is completed, the control means 15 enable operation of the electric servomotor 5 so as to allow rotation and correct angular positioning of the workpiece holder plate 4. This operation is typically performed in a very short time interval, for example 0.5 seconds. Once the correct angular position of the workpiece holder plate 4 is reached, the control means 15 interrupt the power supply to the electric servomotor 5, enable closing of the electric valve 23 so as to allow locking of the workpiece holder plate 4 in the position assumed and then interrupt the power supply of the electric motor 10b. Since the operations described above are performed in a time interval of about ten seconds, the activated electrical devices 5, lOb and 23 draw power

only for this very short period of time and therefore the table has a low power consumption. In this way, the rotary table 1 according to the invention allows 1200 to 1500 positioning cycles to be performed before, it is required to perform recharging or replacement of the batteries 14, corresponding to about 2 to 3 days operation of the work centre. Obviously it is possible to increase the autonomy of the rotary table 1 by means of incorporation of a greater number of batteries 14.

Alternatively, this object may be achieved using an electric or electromagnetic energy source 10 having a smaller power consumption.

From the description provided above by way of example, it can be understood that the rotary table 1 according to the invention, when supported by a pallet 20 of the standard type for work centres, may be advantageously used, without the need for any hydraulic, pneumatic or electrical connection, in a standard work centre, in the case where it is required to have an axis of rotation in addition to that provided by the centre itself. In the same manner, the rotary table 1 supported by a standard pallet 20 may be used in three-axis vertical-spindle work centres if an axis of rotation is required.

Owing to the use of components with a lower power consumption and therefore smaller volume, the dimensions of the rotary table 1 described above, for example 350x500 mm, are compatible with the dimensions of a standard pallet for work centres, for example 500x500 mm.

The height of the rotary table 1, for example 600 mm, is also compatible with use thereof in a standard work centre.

With reference to Figures 9 to 14,100 denotes overall a rotary table in accordance with an alternative embodiment of the present invention. The parts of the table 100, structurally and functionally equivalent to the rotary table 1, are distinguished by the same reference numbers and will not be further described.

In particular, the base body 2 is housed in a workpiece holder turret 101 defined by an upper side 101c and by two side surfaces 101a and 101b able to support workpieces in addition to the workpiece fixed to the workpiece holder plate 4.

In order to control operation of the electric motor 5, the rotary table 100 comprises an electronic control apparatus 18 linked to the control means 15 of the table 100. The rotary table 100 is also able to be mounted on a pallet 20 for work centres and offers the same advantages as the embodiment described above.

As can be appreciated from that described, the rotary table according to the present invention is able to satisfy the requirements and overcome the drawbacks referred to in the introductory part of the present description with reference to the prior art. The advantages arising from the use of the present invention consist mainly in the fact of providing a rotary table able to be equipped and used at any time since it is free of electrical, hydraulic or pneumatic connections.

The rotary table according to the present invention, when installed in a work centre, allows the introduction of a rotating axis in addition to that of the work centre. In particular, the use of the table according to the invention is advantageous when the rotating axis provided by the work centre is insufficient for performing machining operations which require a high degree of precision along the interaxes.

The table according to the invention may be supported by a standard pallet, in the manner of any apparatus, and does not required physical connections with the work centre or with the rotary table of the work centre on which it is to be installed.

Obviously, a person skilled in the art, in order to meet additional and specific requirements, may make numerous modifications and variations to the rotary table according to the invention described above, all of which however are contained within the scope of protection of the invention as defined by the following claims.