DESCRIPTION

The present patent concerns motorized transmission systems with screw shaft and lead screw nut with recirculating balls, and more specifically it concerns an improved transmission system for transmitting the translational motion to a translating carriage.

Systems comprising a fixed frame provided with a carriage which is mounted thereon and is translated along at least one translation direction are known in the art. Motion transmission systems using a screw shaft on which a lead screw nut with recirculating balls is mounted are normally used for moving said carriage, wherein a motor sets the screw shaft or the lead screw nut rotating.

Four different transmission systems of this type are essentially known:

1) Screw shaft rotating on fixed frame and lead screw nut fixed on translating carriage.

In this solution the screw shaft is rotated axially so that the lead screw nut mounted on it translates along the screw shaft. The carriage is integrally constrained to the lead screw nut and thus translates together with it.

2) Screw shaft rotating on translating carriage and lead screw nut fixed on fixed frame.

In this solution, the lead screw nut is integrally constrained to the fixed frame of the system, while the rotary screw shaft is constrained to the translating carriage. The screw shaft is rotated axially and, while rotating within the fixed lead screw nut, it translates in the axial direction and consequently causes also the translation of said translating carriage.

3) Screw shaft fixed on fixed frame and lead screw nut rotating on translating carriage.

In this solution, the screw shaft remains fixed and rigidly constrained to the frame. The lead screw nut, instead, is connected to the translating carriage. When the lead screw nut is set rotating, it translates along the fixed screw shaft, consequently making also said translating carriage translate.

4) Screw shaft fixed on translating carriage and lead screw nut rotating on fixed frame.

In this solution, the screw shaft does not rotate and is integrally constrained to the translating carriage, while the lead screw nut is connected to the fixed frame. When the lead screw nut is set rotating, it causes the translation of the screw shaft, which consequently makes also said translating carriage translate.

All the types of systems described above are usually managed by a numerical control system that controls the motor by means of a specific servo control. More specifically, it controls both the speed and the position through a first rotary encoder positioned on the motor and through a second linear encoder. The position is controlled both during the movement and when the desired position is reached.

All the known transmission systems have, between the motor and the mechanical transmission part, that is, the screw shaft or the lead screw nut, at least one adapter joint or belts with related pulleys, which are inevitably subject to several problems listed below, thus negatively affecting the duration of the system and the positioning precision, both during the movement and when the desired position is reached.

The joint and the driving belt cannot be considered completely rigid, in fact their elasticity is not negligible, which inevitably delays the movement of the controlled screw shaft, thus consequently causing a delay between the expected position and the actual position.

Furthermore, positioning errors take place due to eccentricity errors in the rotation of the pulleys.

Further errors are also caused by the meshing of the belt teeth with the grooves in the pulleys.

In addition to the above, the rotation of the belt generates a high noise, and its inevitable heating causes it to be stretched, which makes its precise positioning on the screw shaft uncertain.

Finally, the wear of the belt makes it necessary to carry out periodic maintenance and replacement activities.

In order to overcome all the drawbacks mentioned above, a new type of motion transmission system for transmitting motion to a translating carriage has been designed and constructed, which comprises a fixed frame, at least one screw shaft, at least one lead screw nut with recirculating balls mounted on said screw shaft, at least one carriage connected to said screw shaft or to said lead screw nut with recirculating balls, and at least one motor suited to set said screw shaft or said lead screw nut with recirculating balls rotating, and wherein said motor is a torque motor and is directly coupled with said screw shaft or said lead screw nut.

The main object of the present invention is to guarantee maximum precision in the positioning of the translating carriage.

Another important object is to reduce the mechanical parts subject to wear, thus also reducing the noise.

These and other direct and complementary objects are achieved by the new transmission system which can be carried out according to four possible embodiments summed up here below.

1) Screw shaft rotating on fixed frame and lead screw nut fixed on translating carriage.

In this solution, the torque motor is directly connected to said screw shaft, which is thus set rotating around its own axis, causing the translation of the lead screw nut and the carriage.

2) Screw shaft rotating on translating carriage and lead screw nut fixed on fixed frame.

Also in this solution, said torque motor is directly connected to said screw shaft which rotates axially and furthermore translates integrally with the carriage. 3) Screw shaft fixed on fixed frame and lead screw nut rotating on translating carriage.

In this solution, said torque motor is connected to said lead screw nut which is thus set rotating around its own axis and with respect to said screw shaft and furthermore is translated together with the carriage.

4) Screw shaft fixed on translating carriage and lead screw nut rotating on fixed frame.

Also in this solution, said torque motor is connected to said lead screw nut, whose rotation causes the translation of the screw shaft and the carriage.

The characteristics of the new transmission system will be better clarified in the following description making reference to the drawings which are attached hereto by way of non-limiting example.

Figure 1 shows a schematic view of the first embodiment of the transmission system (1).

The system (1) comprises a fixed frame (10) and a screw shaft (20) mounted in a rotatable manner on one or more supports (11, 12) which are integral with said frame (10).

Said screw shaft (20), in particular, is mounted on said supports (11, 12) in such a way that it can only rotate around its own longitudinal axis (21).

Said screw shaft (20) is provided with at least one lead screw nut with recirculating balls (30) which is mounted thereon and in turn integrally constrained to a carriage (40) by means of a special support (31).

A torque motor (50) is directly connected to said screw shaft (20).

The rotary motion transmitted to said screw shaft (20) by the motor is transmitted as a linear motion to said lead screw nut (30), which translates in a direction (X) parallel to said axis (21) of the screw shaft (20), pulling along said carriage (40) in its linear motion.

In this solution, said torque motor (50) is thus fixed and integral with the fixed frame (10).

Figure 2 shows a schematic view of the second embodiment of the transmission system (2).

The transmission system (2) comprises a fixed frame (10) on which at least one lead screw nut with recirculating balls (30) is integrally mounted by means of a special support (31).

Said at least one lead screw nut (30) is mounted on a screw shaft (20) which in turn is constrained in a rotatable manner to a carriage (40) by means of one or more supports (11, 12).

More specifically, said screw shaft (20) is mounted on said supports (11, 12) in such a way that it can rotate around its own longitudinal axis (21).

A torque motor (50) is directly connected to said screw shaft (20).

The rotary motion transmitted by the motor (50) to said screw shaft (20) causes an axial translational motion of said screw shaft (20) with respect to said lead screw nut (30) in a direction (X) parallel to said axis (21) of the screw shaft (20).

Therefore, said carriage (40) translates integrally with the screw shaft (20).

In this solution, said torque motor (50) thus translates with respect to the fixed frame (10) integrally with said screw shaft (20).

Figure 3 shows a schematic view of the third embodiment of the transmission system (3).

The transmission system (3) comprises a fixed frame (10) and a screw shaft (20) integrally constrained to said fixed frame (10) by means of special supports (11, 12) in such a way that it can neither translate along its longitudinal axis (21) nor rotate axially.

Said screw shaft (20) is provided with at least one lead screw nut with recirculating balls (30) which is mounted thereon and in turn connected to a carriage (40) by means of a special support (31).

A torque motor (50) is connected to said lead screw nut (30) by means of a special support (51) in such a way as to transmit a rotary motion around the longitudinal axis (21) of the screw shaft (20) to said lead screw nut (30).

The rotary motion transmitted to the lead screw nut (30) causes its translation along said screw shaft (20) and consequently causes the translation of said carriage (40) in the direction (X) parallel to the longitudinal axis (21) of the screw shaft (20).

In this solution, the torque motor (50) translates integrally with the lead screw nut (30) and the carriage (40) with respect to the fixed frame (10).

Figure 4 shows a schematic view of the fourth embodiment of the transmission system (4).

The transmission system (4) comprises a fixed frame (10) with at least one torque motor (50) and at least one lead screw nut with recirculating balls (30) constrained thereto, the latter by means of special supports (31).

Said lead screw nut (30) is mounted on a screw shaft (20) which in turn is fixed to a carriage (40) through supports (11, 12).

Said torque motor (50) is connected to said lead screw nut (30) by means of a special support (51) in such a way as to transmit to said lead screw nut (30) a rotary motion around the longitudinal axis (21) of the screw shaft (20).

The rotary motion transmitted to the lead screw nut (30) causes the translation of said screw shaft (20) along its longitudinal axis (21) and consequently the translation of said carriage (40) along a direction (X) parallel to said longitudinal axis (21) of the screw shaft (20).

In this solution, the motor (50) is thus fixed with respect to the frame (10).

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