Variator device of the angular speed of a driven shaft, in particular of a sewing machine.

The present invention falls within the technical field that refers to the variation of angular speed of a driven shaft with respect to the angular speed of the drive shaft of the same driven shaft, which can be advantageously used in sewing machines, with special reference to machines in which the needle does not determine the forward movement of the material.

As it is known, in this type of machines the needle is exclusively moved vertically, normally by means of a crank and connecting rod mechanism that receives motion from the main shaft; therefore, every revolution of the main shaft corresponds to a complete descending and ascending cycle of the needle.

In a flat sewing machine, for example, for a portion of each cycle the needle is lowered under the plane that supports the material to be sewn, reaching out towards the crochet hook to form the stitch, while for the rest of the cycle it is raised above the said plane. The active phase of the parts responsible for the forward movement of the material to be sewn must be synchronised with the portion of the cycle in which the needle is raised above the same material.

In some models of flat machines, the material to be sewn is fed by a board that moves horizontally according to two orthogonal axes, due to the action of electronically controlled step-by-step motors connected in electronic phase with the electrical motor, provided with encoder, that controls the rotation of the main shaft.

The increase of the machine operation speed reduces the time in which the needle is external to the material and the material must be moved along the distance between two sewing points.

Beyond a certain speed value, the useful time for the forward movement of the material is too short to operate the actuators that move the material-

support board, also due to hysteresis between the transmission of the control signal by the electronic control unit and the start of the action. This causes a limit for the machine operation speed, which is however rather low, beyond which the machine does not operate, with an evident productivity loss.

To increase the said limit, an attempt has been made to electronically control the motor that actuates the needle, in such a way that it accelerates when the needle is in the portion of the cycle in which it is engaged with the material and crochet hook, and it slows down proportionally when it is disengaged from them, in order to increase the time of the relevant portion of cycle.

Also in this case, however, the delays between the control inputs and the action prevent the desired result when rotational speed values increase. The purpose of the present invention is to devise a variator device of the angular speed of a driven shaft of the said sewing machine, associated with the sewing needle, with respect to the one of the drive shaft, in particular to obtain, from each revolution with constant angular speed, a revolution with variable angular speed of the driven shaft, in part at higher speed and in part at lower speed. Another purpose of the invention is to devise a device able to operate at least up to the maximum speed permitted for the sewing machine.

An additional purpose of the invention refers to the construction of a simple inexpensive device that does not require significant structural modifications of the machine where it is installed. The characteristics of the invention will become evident from the following description of a preferred embodiment of the device, according to the contents of the claims and according to the enclosed drawings, wherein:

• Fig. 1 is an axonometric cutaway view of the back of a sewing machine where the device of the invention is installed;

• Fig. 2 is an exploded axonometric view of the parts of Fig. 1 ; • Figs. 3A to 3F illustrate the actuation diagram of the device according to a first configuration, in sequential positions;

• Figs. 4A to 4F illustrate the actuation diagram of the device according to

a second configuration, in the same positions as Figs. 3A to 3F;

• Figs. 5A to 5F illustrate the actuation diagram of the device according to a third configuration, in the same positions as Figs. 3A to 3F;

• Fig. 6 illustrates a diagram of the angular speeds of the main driven shaft with the device in the first configuration;

• Fig. 7 illustrates a diagram of the angular speeds of the main driven shaft with the device in the second configuration;

• Fig. 8 illustrates a diagram of the angular speeds of the main driven shaft with the device in the third configuration; With reference to the aforementioned figures, numeral 1 indicates the device of the invention as a whole.

The device 1 is designed to be associated, for example, to a sewing machine 100 of known type, of which only the back of the head 101 is shown. The machine 100 is a model of machine in which the needle (not shown) does not determine the forward movement of the material and, as mentioned in the premises, is exclusively moved vertically, normally by means of a crank and connecting rod mechanism (not shown) that receives motion from a main shaft 102 supported with horizontal axis by the head 101. Each revolution of the main shaft 102 corresponds to a complete descending and ascending cycle of the needle.

The machines 100 include flat machines, in which the material is fed by a board (not shown) that moves horizontally according to two orthogonal axes due to the action of electronically controlled step-by-step motors, connected in electronic phase with the electrical motor 2, provided with encoder, that controls the rotation of the main shaft 102.

As described in the premises, in the said machines 100, for a portion of each cycle the needle is lowered under the level of the plane that supports the material, reaching out towards the crochet hook to form the stitch, while for the rest of the cycle it is raised above the said plane and above the material to be sewn; evidently, the active phase of the parts designed to move the material forward must be synchronised with the portion of the cycle in which the needle is raised above the material.

The device 1 is mounted between the electrical motor 2 and the main shaft 102 of the machine 100 by means of a U-shaped bracket 3 fixed to the back of the head 101 and designed to support the electrical motor 2 in such a way that the axis A of the drive shaft 20 splined outside the motor 2 is eccentric with respect to the axis B of the main shaft 102 (Figs. 1 and 2).

A first disk 21 is splined on the drive shaft 20, to which a first crank pin 22 is fixed at a predefined radial distance with respect to axis A of the same drive shaft 20. Likewise, a second disk 121 is splined on the main shaft 102, to which a second crank pin 121 is splined and positioned with respect to the axis B of the main shaft 102 at a radial distance equal to the one of the first pin 22 with respect to axis A.

The first and second crank pins 22, 122 are angularly staggered and interconnected by means of a connecting rod 4 with suitable length. The rotational direction R given by the motor 2 (anti-clockwise in Figs. 3Aí3F, 4Aí4F, 5Aí5F) is such that the first crank pin 22 surpasses the second crank pin 122, and therefore the connecting rod 4 is subjected to traction and drives the latter and rotates the main shaft 102 in the same direction. Assuming that the drive shaft 20 and the first crank pin 22 rotate with constant angular speed ωA, the main shaft 102 is given an instantaneous angular speed ωB that for each revolution varies between a higher value and a lower value compared to the said speed ωA.

With suitable tuning of the main shaft 102 and of the associated drive parts, operational cycles of the needle are defined, in which the phase with the needle in lowered position is accelerated and the phase with the needle in raised position is slowed down.

In such a way the time in which the needle is raised in external position to the material is extended to allow for a longer useful phase of the parts designed to move the material forward. The motion law that actuates the main shaft 102 depends on the geometry of the device 1. With reference to the diameter of the circular trajectories C1 , C2 travelled by

the first and second crank pin 22, 122, respectively, in anti-clockwise direction, and the angular stagger of the same pins 22, 122, therefore with reference to the length of the connecting rod 4, the following is defined for axes A and B:

- a first field of permitted eccentricities Edx, in which axis A is on the right of axis B, looking at the mechanism from the electrical motor side 2 (Figs. 1 , 2,

3Aí3F, 4Aí4F);

- a second field of permitted eccentricities Esx, in which axis A is on the left of axis B, looking at the mechanism from the electrical motor side 2 (Figs. 5Aí5F); A first geometrical configuration of the device 1 shown in Figs. 3A-3F falls within the first eccentricity field Edx; the same figures show the position of the second crank pin 122 for each 45° rotational increment of the first pin 22. With reference to the said first configuration, Fig. 6 illustrates the diagram of the angular speeds of the drive shaft 20 (constant ωA) and the main shaft 102 (variable ωB).

A second geometrical configuration of the device 1 shown in Figs. 4Aí4F falls within the first eccentricity field Edx, but with higher value than the first configuration; the same figures show the position of the second crank pin 122 for each 45° rotational increment of the first pin 22. As shown in Fig. 7, the angular speed ωB of the main shaft 102 has a range between the maximum and the minimum value higher than Fig. 6, due to increased eccentricity. A third geometrical configuration of the device 1 shown in Figs. 5Aí5F falls within the second eccentricity field Esx; as in the previous examples, the same figures show the position of the second crank pin 122 for each 45° rotational increment of the first pin 22.

Fig. 8 shows the trend of the angular speed ωB of the main shaft 102 according to the modest eccentricity that oscillates with limited range between the maximum and minimum value. Comparative tests will allow to determine the geometry that originates the most favourable motion law for each specific application, according to the limits imposed by mutual restrictions between the various articulation points of the device. Based on test results, the device of the invention is able to operate without causing significant vibrations in

addition to ordinary ones, including at the maximum rotational speed (approx.

2000 rev/min) of the said sewing machines.

Evidently, the device of the invention allows to achieve the aforementioned purposes, in particular to allow the needle of the sewing machine to slow down when it is raised above the material in order to allow a higher useful time for the actuation of the forward-moving parts.

This advantageous aspect allows to increase the maximum working speed of the machine and consequently its productivity.

Being simple to construct and install, the device of the invention can be applied both to new and existing machines, with limited costs and without requiring any significant structural modification of the machine where it is installed.

In the aforementioned figures, the angular speed of the drive shaft 20 is assumed to be constant; it is understood that the same can be varied, with associated variation of the angular speed ωB of the driven shaft.

Finally, the device as illustrated above can also be applied in machines of any type that require to vary the angular speed of a driven shaft compared to the angular speed of the motor used to actuate the same shaft.

However, it is understood that the foregoing description has an illustrative, not limiting value and therefore any modifications of the device, for instance in the dimensions of its parts, are to be considered as falling within the same protective scope of the following claims.