Machine tool for working pieces powered by a three-phase motor

The present invention relates to a machine tool for working pieces powered by a three-phase motor.

Field of the invention

In particular, the invention relates to the structure of a machine tool for working pieces for domestic or semi-professional use which comprises a three-phase motor and an inverter to control said three-phase motor.

More specifically, the inverter is powered single phase and is connected to the three-phase motor.

The inverter can be positioned anywhere on the machine tool.

For example, the inverter can be placed outside or inside a basement of the machine tool.

The machine tool can be a single-function machine tool or a combination machine tool.

A single-function machine tool can be a saw or a spindle moulder or a planer.

A combination machine tool is a machine tool comprising a plurality of tools and a respective three-phase motor for each tool of said plurality of tools, in which only one tool can operate at a time.

Consequently, said machine tool is designed to start the three-phase motor associated with the tool to be used to machine a piece.

In a first example, a combination machine tool may comprise a saw and a spindle moulder, wherein only the saw or only the spindle moulder can operate.

In a second example, the machine tool can comprise a saw and a planer, wherein only the saw or only the planer can operate.

In a third example, the machine tool can comprise a spindle moulder and a planer, wherein only the spindle moulder or only the planer can operate.

In a further example, the machine tool can comprise a saw, a spindle moulder and a planer, wherein only the saw or only the spindle moulder or only the planer can operate.

Prior art

In the context of machine tools for machining pieces for domestic or semi-professional use or where there is no three-phase network, a machine tool is powered by a single-phase motor.

A first disadvantage of said known machine tool is due to the presence of one or more capacitors in the single-phase motor.

The presence of one or more capacitors in a single-phase motor causes limited efficiency and therefore reduced performance, as well as vibrations that interfere with the machining of a workpiece (such as a panel made of wood or other material) with the consequent decrease in the quality of machining.

It may be considered that a single-phase motor requires testing before being sold and that the testing time takes into account the need to carry out a test to monitor vibrations.

A second disadvantage due to the presence of said capacitors in a single-phase motor is given by the risk that a capacitor can explode when said capacitor is worn out.

For this reason, a capacitor periodically needs to be replaced with a new capacitor.

However, replacing a capacitor with a new capacitor is not a simple operation since an operator runs the risk of receiving an electric shock, even though the machine tool is not connected to an electrical network.

Furthermore, it is not easy to find capacitors on the market, especially in the US or Canadian market.

A third disadvantage is given by the fact that said machine tool is provided with a brake to stop said single-phase motor, which can be an electronic brake or a mechanical brake.

On the one hand, an electronic brake must be certified to be used in machine tools marketed in some countries and often due to regulations in these countries it cannot be certified.

On the other hand, a mechanical brake needs to be adjusted periodically and replaced when it has reached its maximum lifetime.

However, even replacing a mechanical brake with a new mechanical brake is not a simple operation and requires the intervention of an operator.

Aim of the invention

The aim of the present invention is to overcome said disadvantages, providing a machine tool comprising a first three-phase motor and an inverter to control said first three-phase motor, so as to avoid the use of capacitors and significantly reduce vibrations and improve the quality of machining of a workpiece, such as a panel made of wood or other material.

A further aim of the invention is to provide a machine tool having a simplified structure compared to a machine tool of a known type.

In fact, the machine tool can comprise a plurality of three-phase motors, based on the number of tools with which it is provided (i.e. a three- phase motor for each tool) but a single inverter to control a three-phase motor of said plurality of three-phase motors at a time.

Object of the invention

It is object of the invention a machine tool for working a piece, comprising:

- a first tool for working said piece,

- a first three-phase motor to power said first tool, and

- an inverter to control said first three-phase motor, wherein said inverter is powered single-phase and is connected to said first three-phase motor.

In a first alternative, said machine tool comprise a start/stop circuit for starting/stopping said first three-phase motor, and a power supply circuit to power said first three-phase motor. Furthermore, said inverter can be connected to said start/stop circuit and, through said power supply circuit, to said first three-phase motor.

In particular, said start/stop circuit can be configured to send a stop signal to said inverter for stopping said first three-phase motor, and said inverter can be configured to receive said stop signal and impose, through said power supply circuit, a first deceleration over time on said first three- phase motor, so that said first three-phase motor stops.

Furthermore, the machine tool can comprise:

- alarm means for emitting an alarm signal,

- storage means in which at least one value associated with a motor nameplate datum referred to said first three-phase motor is stored, and

- a logic control unit, connected to said alarm means and to said storage means and configured to activate said alarm means when a value of a motor nameplate datum referred to said first three-phase motor is greater than a value associated with the corresponding motor nameplate datum stored in said storage means or greater than a value associated with the corresponding motor nameplate datum stored in said storage means for a time greater than a predetermined time or in case of an anomaly.

The machine tool mentioned above can be a saw machine or a spindle or a planer machine.

In a second alternative, the machine tool can comprise:

- a second tool for working said piece, different from said first tool, and

- a second three-phase motor to power said second tool,

- a power supply circuit to power said first three-phase motor and said second three-phase motor.

Said inverter is connected, through said power supply circuit, to said first three-phase motor and to said second three-phase motor.

Furthermore, said machine tool can comprise a start/stop circuit for starting/stopping said first three-phase motor and said second three-phase motor, so that said first three-phase motor is stopped before starting said second three-phase motor or that said second three-phase motor is stopped before starting said first three-phase motor.

Said start/stop circuit can be configured to send a stop signal to the inverter to stop said first three-phase motor or said second three-phase motor, and the inverter can be configured to receive the stop signal sent by said start/stop circuit and impose, through said power supply circuit, a first deceleration over time to the first three-phase motor, so that said first three- phase motor stops, or a second deceleration over time to the second three- phase motor, so that said second three-phase motor stops.

In particular, said start/stop circuit can comprise:

- a first contactor, arranged between said inverter and said first three-phase motor, in which said first contactor is configured to switch from an open state, in which it prevents the passage of an electric current from said inverter to said first three-phase motor, and a closed state, in which it allows the passage of an electric current from said inverter to said first three-phase motor, and

- a second contactor arranged between said inverter and said second three- phase motor, in which said second contactor is configured to switch from an open state, in which it prevents the passage of an electric current from said inverter to said second three-phase motor, and a closed state, in which it allows the passage of an electric current from said inverter to said second three-phase motor.

Advantageously, said inverter can have a safety function called GDL function configured so that each contactor switches from a closed state to an open state after a respective predetermined time period At, so that the stopping of said first three-phase motor is completed before starting said second three-phase motor or that the stopping of the second three-phase motor is completed before starting said first three-phase motor.

Furthermore, the machine tool can comprise:

- alarm means for emitting an alarm signal, - storage means in which at least one value associated with a motor nameplate datum referred to said first three-phase motor and at least one value associated with a motor nameplate datum referred to said second three-phase motor is stored, and

- a logic control unit, connected to said alarm means and to said storage means and configured to activate said alarm means when, with reference to the first three-phase motor, a value of a motor nameplate datum referred to said first three-phase motor is greater than a value associated with the corresponding motor nameplate datum stored in said storage means or greater than a value associated with the corresponding motor nameplate datum stored in said storage means for a time greater than a predetermined time or in case of an anomaly, and with reference to the second three-phase motor, when a value of a motor nameplate datum referred to said second three-phase motor is greater than a value associated with the corresponding motor nameplate datum stored in said storage means or greater than a value associated with the corresponding motor nameplate datum stored in said storage means for a time greater than a predetermined time or in the event of an anomaly.

With reference to the tools, the first tool can be a spindle moulder and the second tool is a saw.

Regardless of the first alternative or the second alternative, the machine tool can comprise a working table for working a piece and a basement for supporting said working table, and the inverter can be positioned outside said basement or inside said basement.

Furthermore, said machine tool can be a semi-professional machine tool or a machine tool for domestic use.

Figure list

The present invention will be now described, for illustrative, but not limitative purposes, according to its embodiments, making particular reference to the enclosed figures, wherein: Figure 1 is a perspective view, partially in transparency, of a first embodiment of a machine tool which is a saw machine, in which said machine tool includes a three-phase motor and an inverter and said inverter is positioned outside the basement of said machine tool;

Figure 2 is a perspective view of the machine tool of Figure 1 without transparent parts;

Figure 3 is a front view of the machine tool of figure 2;

Figure 4 is a side view of the machine tool of figure 2;

Figure 5 is a perspective view of a variant of the first embodiment of the machine tool of Figure 1 , in which the inverter is positioned inside the basement of said machine tool;

Figure 6 is a front view of the machine tool of Figure 5;

Figure 7 is a side view of the machine tool of Figure 5;

Figure 8 is a partially transparent perspective view of a second embodiment of a machine tool which is a spindle, wherein said machine tool includes a three-phase motor and an inverter and said inverter is positioned outside the basement of said machine tool;

Figure 9 is a perspective view of the machine tool of Figure 8 without transparent parts;

Figure 10 is a front view of the machine tool of Figure 9;

Figure 11 is a side view of the machine tool of Figure 9;

Figure 12 is a partially transparent perspective view of a variant of the second embodiment of the machine tool of Figure 8, in which the inverter is positioned inside the basement of said machine tool;

Figure 13 is a perspective view of the machine tool of Figure 12 without transparent parts;

Figure 14 is a front view of the machine tool of Figure 12;

Figure 15 is a side view of the machine tool of Figure 12;

Figure 16 is a partially transparent perspective view of a third embodiment of a machine tool which is a planer machine, in which said machine tool includes a three-phase motor and an inverter and said inverter is positioned outside the basement of said machine tool;

Figure 17 is a perspective view of the machine tool of Figure 16 without transparent parts;

Figure 18 is a front view of the machine tool of Figure 16;

Figure 19 is a side view of the machine tool of Figure 16;

Figure 20 is a view of a variant of the third embodiment of the machine tool of Figure 16, in which the inverter is positioned inside the basement of said machine tool;

Figure 21 is a side view of the machine tool of Figure 20;

Figure 22 is a schematic view of an inverter connected to a start/stop circuit for starting/stopping a three-phase motor of the machine tool and to a power supply circuit to power said first three-phase motor;

Figure 23 is a partially transparent perspective view of a fourth embodiment of a machine tool which is a combination machine tool comprising a first tool and a second tool, as well as a first three-phase motor to power said first tool and a second three-phase motor to power said second tool and a single inverter, positioned outside the basement of said machine tool;

Figure 24 is a schematic view of an inverter connected to a start/stop circuit for starting/stopping the first three-phase motor or the second three- phase motor of the combination machine tool of Figure 23 and to a power supply circuit for powering said first three-phase motor or said second three- phase motor.

Detailed description of the invention

With reference to Figures 1 to 7, 8 to 15, and 16 to 21 , a respective machine tool for working a piece comprising a first tool, a first three-phase motor and an inverter is described.

Regardless of the type of tool, the machine tool comprises a three- phase motor to power said tool and an inverter to control said three-phase motor.

Said piece can be a panel of wood or other material.

With particular reference to Figures 1 - 4, a first embodiment of a machine tool indicated with the numerical reference 1 is described.

Said machine tool 1 comprises:

- a first tool S for working said piece,

- a first three-phase motor 2 to power said first tool S, and

- an inverter 3 to control said first three-phase motor 2.

Said inverter 3 is powered single-phase and connected to said first three-phase motor 2.

In particular, said inverter 3 has a three-phase output which is connected to said first three-phase motor 2.

Said machine tool 1 comprises a working table 4 for working said piece and a basement 5 to support said working table 4.

In particular, in the first embodiment being described, said inverter 3 is positioned outside said basement 5.

Furthermore, in the first embodiment being described, said first tool S is a saw, in particular a circular saw, and said machine tool is a saw machine.

In the first embodiment being described, with reference to Figures 2 to 4, said saw is in an operational position for working a piece.

In particular, said saw is movable between a rest position, in which it is placed inside the basement 5, and an operational position, in which said saw partially protrudes with respect to the working table 4.

Said working table 4 is provided with a slot to allow the saw to exit from the working table.

Figures 5 to 7 show a variant of the first embodiment.

Differently from the first embodiment, in said variant, the inverter 3 is inside the basement 5 of the machine tool 1 .

Figures 8 to 11 show a second embodiment of a machine tool for working a piece indicated with the numerical reference 10.

Said machine tool 10 comprises:

- a first tool T for working said piece,

- a first three-phase motor 20 to power said first tool T, and

- an inverter 30 to control said first three-phase motor 20.

In particular, said inverter 30 is powered single-phase and has a three- phase output connected to said first three-phase motor 20.

Said machine tool 10 comprises a working table 40 for working said piece and a basement 50 for supporting said working table 40.

In particular, in the second embodiment being described, said inverter 30 is positioned outside said basement 50.

In the second embodiment being described, said first tool T is a spindle moulder and said machine tool 10 is a spindle.

In the second embodiment being described, with reference to Figures 9 to 11 , said spindle moulder is in an operational position for machining a piece.

In particular, said spindle moulder is movable between a rest position, in which it is arranged inside the basement 50, and an operational position, in which said spindle moulder protrudes at least partially (i.e. partially or totally) with respect to the working table 40.

Said working table 40 is provided with a seat to receive the spindle moulder, so that in the rest position the spindle moulder is inside said seat.

Figures 12 to 15 show a variant of the second embodiment.

Differently from the second embodiment, in said variant, the inverter 30 is inside the basement 50 of the machine tool 10.

Figures 16 to 19 show a third embodiment of a machine tool for working a piece indicated with the numerical reference 100.

Said machine tool 100 comprises:

- a first tool P for working said piece,

- a first three-phase motor 120 to power said first tool P, and - an inverter 130 to control said first three-phase motor 120.

In particular, said inverter 130 is powered single phase and has a three-phase output connected to said first three-phase motor 120.

Said machine tool 100 comprises a working table 140 for working said piece and a basement 150 for supporting said working table 140.

In particular, in the third embodiment being described, said inverter 130 is positioned outside said basement 150.

In the third embodiment being described, said first tool P is a planer and said machine tool 100 is a planer machine.

Figures 20 and 21 show a variant of the third embodiment.

Differently from the third embodiment, in said variant, the inverter 130 is inside the basement 150 of the machine tool 100.

Regardless of the machine tool 1 , 10, 100 described above, as shown in Figure 22, each machine tool 1 , 10, 100 comprises an inverter 3, 30, 130, a start/stop circuit CMA for starting/stopping said first motor three-phase motor 2, 20, 120, and a power supply circuit CP to power said first three- phase motor 2, 20, 120.

The inverter 3, 30, 130 is connected to start/stop CMA and to the power supply circuit CP.

Furthermore, the inverter 1300 is connected to said three-phase motor 2, 20, 120 through said power supply circuit CP.

The start/stop circuit CMA starts/stops the first three-phase motor 2, 20, 120 through the inverter 3, 30, 130.

In particular, the start/stop circuit CMA comprises a control circuit (not shown) to control the inverter 3 which in turn controls said first three-phase motor 2, 20, 120 so that said first three-phase motor 2, 20, 120 is started or stopped.

In other words, the control circuit controls the inverter 3 and the inverter 3 controls the first three-phase motor 2, 20, 120.

The power circuit CP provides power to the first three-phase motor 2, 20, 120 to start said first three-phase motor 2, 20, 120 or does not provide power to stop said three-phase motor 2, 20, 120.

For each machine tool 1 , 10, 100, the inverter s, 30, 130 is connected to the respective first three-phase motor 2, 20, 120 through the respective power supply circuit CP.

In order to stop the first three-phase motor 2, 20, 120 of each machine tool 1 , 10, 100, the start/stop circuit CMA is configured to send (via the control circuit) a stop signal to the inverter 3, 30, 130 to stop said first three-phase motor 2, 20, 120, for example in the case of an anomaly/emergency or in the case in which the machining of a piece, through the tool moved by the first three-phase motor 2, 20, 120, is finished.

The inverter 3, 30, 130 is configured to receive the stop signal sent by the start/stop circuit CMA and impose, through said power supply circuit CP, a first deceleration over time to the first three-phase motor 2, 20, 120, so that said first three-phase motor 2, 20, 120 stops.

A predetermined first deceleration ramp is associated with said first deceleration.

Consequently, said predetermined first deceleration ramp has a predetermined first profile.

In other words, the inverter reduces the frequency of the supply voltage of the first three-phase motor 2, 120, 120 over time until the first three-phase motor actually stops.

For example, with reference to a 50Hz three-phase motor, to stop said three-phase motor in less than 7 seconds, the deceleration may be a deceleration of 8Hz per second.

Regulations require that a tool stop working within a certain time.

In general, a predetermined time is established within which the three- phase motor must stop so that the tool stops in the time required by the regulations.

Furthermore, the inverter 3, 30, 130 is configured to control the deceleration of the first three-phase motor 2, 20, 120 until the first three- phase motor completely stops.

Due to the stopping of the first three-phase motor 2, 20, 120, also the movement of the tool stops.

The control circuit is a circuit of a known type and comprises a first electric branch to allow or prevent the passage of an electric current from the start/stop circuit CMA to the inverter 3, 30, 130 (to control the inverter so that the first three-phase motor 2, 20, 120, is powered).

Said first electric branch comprises a switch that switches from a closed state, in which the passage of electric current from the start/stop circuit CMA to the inverter 3, 30, 130 is allowed, to an open state, in which the passage of electric current from the start/stop circuit CMA to the inverter 3, 30, 130 is prevented, and vice versa.

In general, the machine tool 1 , 10, 100 is provided with a first button to start the first three-phase motor 2, 20, 120, as well as at least one stop button to stop said first three-phase motor 2, 20, 120.

Regardless of the three embodiments described above and their respective variants, the machine tool can comprise:

- alarm means for emitting an alarm signal,

- storage means (for example a memory) in which at least one value associated with a motor nameplate datum referred to the respective first three-phase motor 2; 20; 120 is stored, and

- a logic control unit, connected to said alarm means and to said storage means and configured to activate said alarm means when a value of a motor nameplate datum, referred to said first three-phase motor 2, 20, 120, is greater than a value associated with the corresponding motor nameplate datum stored in said storage means or greater than a value associated with the corresponding motor nameplate datum stored in said storage means for a time greater than a predetermined time (said predetermined time can be established a priori by an operator based on needs and stored in said storage means) or in case of an anomaly, for example when the inverter 3, 30, 130 is not connected to the first three- phase motor 2, 20, 120.

Said alarm means can comprise at least one light source for emitting a light radiation.

A given motor nameplate can be chosen from the following motor nameplate data group: rated frequency, rated power, rated speed (engine revolutions per minute), etc..

Figure 23 shows a fourth embodiment of a machine tool for working a piece indicated with the numerical reference 1000.

In particular, said machine tool 1000 is a combination machine tool comprising a first tool S and a second tool T, different from said first tool S, as well as a first three-phase motor 1200A to power said first tool S and a second three-phase motor 1200B to power said second tool T and a single inverter 1300 to control said first three-phase motor 1200A and said second three-phase motor 1200B (one at a time).

Advantageously, in the fourth embodiment described, the machine tool comprises a single inverter 1300 although the machine tool 1000 comprises two different three-phase motors.

As shown in Figure 24, said machine tool further comprises a start/stop circuit CMA for starting/stopping said first three-phase motor 1200A and said second three-phase motor 1200B, such that said first three-phase motor 1200A is stopped before starting said second three-phase motor 1200B or that said second three-phase motor 1200B is stopped before starting said first three-phase motor 1200A (depending on the three-phase motor in use to be stopped to start the other three-phase motor to be used), as well as a power supply circuit CP to power said first three-phase motor 1200A and said second three-phase motor 1200B.

The inverter 1300 is connected to the start/stop circuit CMA and the power supply circuit CP. Furthermore, the inverter 1300 is connected to said first three-phase motor 1200A and to said second three-phase motor 1200B via said power supply circuit CP.

The start/stop circuit CMA starts/stops the first three-phase motor 1200A and the second three-phase motor 1200B through the inverter 1300.

In particular, the start/stop circuit CMA comprises a control circuit (not shown) to control the inverter 1300 which in turn controls the first three- phase motor 1200A and the second three-phase motor 1200B (based on a signal sent by the circuit control) so that said first three-phase motor 1200A is stopped before starting said second three-phase motor 1200B and said second three-phase motor 1200B is stopped before starting said first three- phase motor 1200A.

In other words, the control circuit can control the inverter 1300 so that the first three-phase motor 1200A is stopped and the second three-phase motor 1200A is started or the control circuit can control the inverter 1300 so that the second three-phase motor 1200B is stopped and the first 1200A three-phase motor is started.

Consequently, it is not possible for two three-phase motors to operate concurrently.

In fact, when the first three-phase motor 1200A is in use and needs to be stopped, the start/stop circuit CMA sends (via the control circuit) a stop signal to the inverter 1300 to stop the first three-phase motor 1200A (for example in the case of an anomaly/emergency or in the event that the machining of a piece, via a first tool moved by said first three-phase motor 1200A, is finished) and the inverter 1300 imposes a first deceleration over time on the first three-phase motor 1200A, so that said first three-phase motor 1200A stops.

When the second three-phase motor 1200B is in use and needs to be stopped, the start/stop circuit CMA sends (via the control circuit) a stop signal to the inverter 1300 to stop the second three-phase motor 1200B (for example in the case of an anomaly/emergency or in the event that the machining of a piece, using a second tool moved by said second three- phase motor 1200B, is finished) and said inverter 1300 imposes a second deceleration overtime on the second three-phase motor 1200B, so that said second three-phase motor 1200B stops.

Therefore, in order to stop the first three-phase motor 1200A or the second three-phase motor 1200B, the start/stop circuit CMA is configured to send a stop signal to the inverter 1300 to stop said first three-phase motor 1200A or said second three-phase motor 1200B.

The inverter 1300 is configured to receive the stop signal sent by the start/stop circuit CMA and impose, via said power circuit CP, a first deceleration over time to the first three-phase motor 1200A, so that said first three-phase motor 1200A stops, or a second deceleration over time to the second three-phase motor 1200B, so that said second three-phase motor 1200B stops.

A predetermined first deceleration ramp is associated with said first deceleration.

Consequently, said predetermined first deceleration ramp has a predetermined first profile.

A predetermined second deceleration ramp is associated with said second deceleration.

Consequently, said predetermined second deceleration ramp has a predetermined second profile.

Preferably, said first predetermined deceleration ramp is equal to said second predetermined deceleration ramp.

In other words, the inverter reduces over time the frequency of the supply voltage of the first three-phase motor 1200A until the first three- phase motor actually stops or the frequency of the supply voltage of the second three-phase motor 1200B until the first three-phase motor actually stops. Furthermore, the inverter 1300 is configured to control the deceleration of the first three-phase motor 1200A until said first three-phase motor 1200A actually stops and the deceleration of the second three-phase motor 1200B until said second three-phase motor 1200B actually stops.

The control circuit is a circuit of a known type and comprises a first electric branch and a second electric branch electrically connected to each other in such a way that, when an electric current flows in said first electric branch (to control the inverter 1300 so that the first three-phase motor 1200A is powered), the second electric branch does not allow the passage of electric current (to control the inverter 1300 so that the second motor 1200B is powered), and that, when an electric current flows in said second electric branch (to control the inverter 1300 so that the second three-phase motor 1200B is powered), the first electric branch does not allow the passage of electric current (to control the inverter 1300 so that the first motor 1200A is powered).

Each electric branch comprises a respective switch that switches from a closed state, in which the passage of electric current from the start/stop circuit CMA to the inverter 1300 is allowed, to an open state, in which the passage of electric current from the start/stop circuit CMA to the inverter 1300 is prevented, and vice versa.

In general, the machine tool 1000 is provided with a first button to start the first three-phase motor 1200A, a second button to start the second three-phase motor 1200B, as well as at least one stop button to stop said first three-phase motor 1200A or said second three-phase motor 1200B (since only one three-phase motor between said two three-phase motors will be in operation).

When an operator presses the first button, a first electric current flows in the first electric branch so that the inverter 1300 controls the start of the first three-phase motor 1200A.

When an operator presses the second button, a second electric current flows in the second electric branch so that the inverter 1300 controls the start of the second three-phase motor 1200B.

In particular, said power supply circuit CP comprises:

- a first contactor CA, arranged between said inverter 1300 and said first three-phase motor 1200A, in which said first contactor CA is configured to switch from an open state, in which it prevents the passage of an electric current from said inverter 1300 to said first three-phase motor 1200A, and a closed state, in which it allows the passage of an electric current from said inverter 1300 to said first three-phase motor 1200A, and

- a second contactor CB arranged between said inverter 1300 and said second three-phase motor 1200B, in which said second contactor CB is configured to switch from an open state, in which it prevents the passage of an electric current from said inverter 1300 to said second three-phase motor 1200B, and a closed state, in which it allows the passage of an electric current from said inverter 1300 to said second three-phase motor 1200B.

Furthermore, said inverter 1300 has a safety function called GDL function configured so that each contactor CA, CB switches from a closed state to an open state after a respective predetermined time period At, so that the stopping of said first three-phase motor 1200A is completed before starting said second three-phase motor 1200B or that the stopping of the second three-phase motor 1200B is completed before starting said first three-phase motor 1200A.

In other words, the safety function mentioned above allows to maintain a self-holding on one of the contactors present in the start/stop circuit CMA, based on the tool in use, so as to guarantee the stop of the first tool in use before the second tool is used or the stop of the second tool in use before the first tool is used.

Furthermore, said machine tool 1000 comprises a working table 1400 for working said piece and a basement 1500 for supporting said working table 1400. In particular, in the fourth embodiment being described, said inverter 1300 is positioned outside the basement 1500.

However, although not shown, said inverter 1300 can be positioned inside the basement 1500, without departing from the invention.

Furthermore, in the fourth embodiment being described, said first tool S is a saw, in particular a circular saw, and said second tool T is a spindle moulder.

With reference to the saw, said saw is movable between a rest position, in which it is placed inside the basement 1500, and an operational position, in which said saw partially protrudes with respect to the working table 1400.

Said working table 1400 is provided with a slot to allow the saw to protrude from the working table itself.

With reference to the spindle moulder, said spindle moulder is movable between a rest position, in which it is arranged inside the basement 1500, and an operational position, in which said spindle moulder protrudes at least partially (i.e. partially or totally) with respect to the working table 1400.

Said working table 1400 is provided with a seat to receive the spindle moulder in the rest position.

The machine tool 1000 can comprise:

- alarm means for emitting an alarm signal,

- storage means (for example a memory) in which at least one value associated with a motor nameplate datum referred to the respective three- phase motor 1200A,1200B is stored, and

- a logic control unit, connected to said alarm means and to said storage means and configured to activate said alarm means when: with reference to the first three-phase motor 1200A in use, a value of a motor nameplate datum referred to said first three-phase motor 1200A is greater than a value associated with the corresponding motor nameplate datum stored in said storage means or greater than a value associated with the corresponding motor nameplate datum stored in said storage means for a time greater than a predetermined time (wherein said predetermined time is established based on needs) or in case of an anomaly, for example when the inverter 1330 is not connected to the first three-phase motor 1200, and with reference to the second three-phase motor 1200B in use, when a value of a motor nameplate datum referred to said second three-phase motor 1200B is greater than a value associated with the corresponding motor nameplate datum stored in said storage means or greater of a value associated with the corresponding motor nameplate datum stored in said storage means for a time greater than a predetermined time or in the event of an anomaly, for example when the inverter 1300 is not connected to the second three-phase motor 1200B.

Said alarm means can comprise at least one light source for emitting a light radiation.

A motor nameplate datum can be chosen from the following motor nameplate data group: rated frequency, rated power, rated speed (engine revolutions per minute), etc..

Advantages

Advantageously, from an electromechanical point of view, the machine tool object of the invention has a simplified structure compared to a machine tool of a known type.

In particular, the machine tool object of the invention has no capacitors, so that vibrations are significantly reduced, and has no mechanical brake.

The reduction of vibrations allows a better quality of machining of a workpiece.

For example, the cutting quality of a wooden panel improves when vibrations are significantly reduced.

A second advantage of the machine tool object of the invention, due to the fact that said machine tool comprises a three-phase motor, is that the three-phase motor allows to save space. This is due to a smaller number of electrical cables compared to the number of electrical cables needed for a single-phase motor and the absence of electromechanical components of significant dimensions.

Furthermore, a three-phase motor is lighter and easier to mount in a machine tool than a single-phase motor provided with a mechanical brake.

A further advantage of the machine tool object of the invention, due to the fact that said machine tool comprises an inverter to control the three- phase motor, is that the inverter guarantees a smooth and progressive starting of the three-phase motor, so that the wear of the some mechanical parts is reduced.

For example, the machine tool can be provided with belts and pulleys, and the use of an inverter reduces noise due to contact between a belt and a pulley.

Furthermore, the presence of an inverter prevents an electric current from reaching values that could generate an electric current overload.

Considering that in a laboratory there may be additional machine tools and/or one or more electromechanical devices, in which said machine tool, said additional machine tools and said electromechanical devices are connected to an electrical network, a possible electric current overload in said machine tool risks compromising the functioning of said machine tools and/or said electromechanical devices.

The inverter also guarantees to save energy.

A further advantage due to the presence of an inverter is given by the possibility of using a compact and lightweight three-phase motor.

Another advantage is given by the possibility of generating an alarm signal when the value of at least one motor plate datum referring to the three-phase motor of the machine tool is exceeded.

Furthermore, the inverter has a safety function, i.e. the GDL function, configurable via software which allows an operator to set a minimum time before a contactor switches to the open state based on the tool in use so that the movement of said tool is effectively stopped before a further tool (other than said tool) is used. In case the machine tool is a combination machine tool, i.e. a machine tool comprising at least two tools (where only one tool can be used at a time), this safety function allows an operator to be confident that the three- phase motor causing the movement of the tool in use and which he wishes to stop (to use another tool) has actually stopped. In other words, the safety function of the inverter mentioned above allows to maintain a self-holding on one of the contactors based on the tool in use, so as to guarantee the stopping of the tool in use before a further tool of the same machine tool be used.

The present invention has been described for illustrative, but not limitative purposes, according to its preferred embodiment, but it is to be understood that variations and/or modifications can be carried out by a skilled in the art, without departing from the scope thereof, as defined according to enclosed claims.