The present Invention relates to an electrical generator of pushbutton type.

It is known in the art to form generator devices comprising a pushbutton movable under the action of an external force, a magnet rigidly connected to the pushbutton, and an electrical winding within which the magnet induces an electric current during its operation.

The pushbutton is movable between a rest position and a pressed position. An electric voltage pulse is generated within the winding at each press and at each release of the pushbutton.

These known devices comprise a spring which constantly urges the pushbutton towards the rest position such that, following a pressing action, the pushbutton/magnet unit is able to return to its initial start position. These known devices have however a complex and costly structure.

In particular, a return spring has to be provided, acting on the pushbutton. Moreover, passage of the pushbutton from its rest to its pressed position is not smooth and immediate because the force of the return spring increases while the pushbutton is being pressed towards its completely pressed position.

This results in a certain irregularity in the shape and duration of the electric voltage pulses as the force applied to the pushbutton varies. Moreover the pushbutton generators of this type normally have a certain bulk, in particular in the direction of the pushbutton movement. An object of the invention is to eliminate these drawbacks by providing an electrical generator having a simple and economical structure and a small number of components.

Another object of the invention is to provide an electrical generator provided with a pushbutton able to pass rapidly from the rest position to the pressed position when the force applied to the pushbutton reaches the predetermined threshold.

These and other objects which will be apparent from the ensuing description are attained according to the invention by an electrical generator as described in claim 1.

A preferred embodiment of the present invention and some variants thereof are further clarified hereinafter with reference to the accompanying drawings, in which:

Figure 1 is an exploded perspective view of a first embodiment of the generator of the invention,

Figure 2 is a section therethrough with the pushbutton in the pressed position, Figure 3 shows it in the same view as Figure 2 but with the pushbutton in the rest position, Figures 4-6 show alternative forms of the pushbutton according to the invention, Figure 7 is an exploded perspective view showing a variant of the generator,

Figure 8 is a section through the assembled generator with the pushbutton shown not pressed, Figure 9 is a section through the generator with the pushbutton shown pressed,

Figure 10 is a partially exploded front view of the generator of Figure 8, Figure 11 is a plan section through the generator casing, Figure 12 is a perspective view of the generator pushbutton, Figure 13 is a plan view of the ferromagnetic core, and Figure 14 is a perspective view of the movable portion of the magnetic circuit.

As can be seen from the figures, the electrical generator, indicated overail by 10, consists of an outer cylindrical casing 11 housing a pushbutton

12 movable relative to the casing between a rest position and a pressed position, a cylindrical magnet 15, and an electrical winding 14 disposed in proximity to the magnet such as to be traversed by its magnetic flux.

The generator also comprises a ferromagnetic core 13, associated with the electrical winding 14 and arranged to magnetically attract the magnet 15 in the direction of the pushbutton 12.

The magnet 15 is movable between a first position close to the core 13 and a second position distant from the core, to induce an electric voltage in the winding 14. The movement of the magnet 15 takes place under the action of a force applied to the pushbutton, by virtue of the presence of shanks 16, projecting from the pushbutton 12, which embrace the ferromagnetic core 13 and act on the magnet 15 such as to cause it to withdraw from the core 13 when the pushbutton is pressed. The casing 11 is of hollow cyϊindrica! shape with two apertures 17 and 25 at its opposite ends, i.e. in the position of the magnet 15 and of the pushbutton 12 respectively.

!n proximity to the front aperture 25 the casing 11 presents on its inner waϋ a tooth 24 forming a limit stop for the pushbutton 12 (see Figures 2 and 3),

The pushbutton 12 presents a front portion 22 of reduced diameter at the aperture 25, which terminates with a pushbutton front surface 40 intended to be pressed, for example under the action of a user's finger or of any pressing force. The pushbutton 12 presents a shoulder 23 arranged to cooperate with the tooth 24 to prevent the pushbutton 12 from withdrawing from the casing 11 frontwards,

The ferromagnetic core 13 comprises a head 28 from which a central shank 20 and two lateral shanks 26, 27 project longitudinally. The electrical winding 14, formed for example from a cylindrical coil of electrically conducting wire, is mounted about the centra! shank 20.

The outer shanks 28, 27 embrace the winding 14 on opposite sides and are separated by two slots 18 and 19 on the opposite sides of the core (Figure 1). The shank 27 presents a radial slot 21 intended for the passage of the outward-directed terminal 29 of the winding 14.

The core 13 is secured to the inner wall of the casing 11 at the outer lateral faces of the shanks 26 and 27, for example by forcing, by gluing or by other fixing systems. The core 13 forms with its head 28 a limit stop for the pushbutton 12 in the completely pressed position. As shown in Figure 3, the length of the shanks 18 is chosen such that when the pushbutton 12 is in its rest position, the magnet 15 is in contact with the ferromagnetic core 13.

Figures 2 and 3 show the two operative positions of the generator, with the pushbutton pressed and with the pushbutton in its rest position respectively.

In the configuration shown in Figure 2 the pushbutton is pressed to abut against the ferromagnetic corer 13. The magnet 15 is urged away from the core 13 by the shanks 16 against the action of the attractive force between the magnet and the core 13.

During the movement of the magnet 15 an electric voltage is generated at the terminals 29 of the generator winding.

Passage from the rest position to the pressed position takes place with a smooth snap movement when the force impressed on the pushbutton 12 exceeds a predetermined threshold by virtue of the fact that the magnetic attractive force decades rapidly on detaching the magnet 15 from the core 13.

This ensures an electric voltage of predetermined intensity and duration at the generator terminals.

When force is removed from the pushbutton 12, the magnet 15 returns to its initial configuration of Figure 3 under the action of the magnetic attractive force until it touches the core 13. The pushbutton 12 is urged into the rest position by the shanks 16.

By impressing an oscillating force on the pushbutton a series of alternating voltage pulses is obtained, which are of one sign when the pushbutton is pressed and of opposite sign when the pushbutton is released. !n the embodiment shown in Figure 4 the generator 110 comprises a single arm 116 which passes axiaiiy through the ferromagnetic core 113 and the winding 114, The ferromagnetic core 113 comprises a first inner cylindrical wall embracing the arm 116, an outer cylindrical wall in contact with the outer casing 111 and an annular head portion connecting the two walls together.

The electrical winding 114 is held between the two cylindrical wails by the core 113.

In the generator shown in Figure 5 the means for transmitting the pushbutton force to the magnet comprise a single arm 216 coaxial to the casing 211 , which passes through the core 213 and the winding 214.

In this case the ferromagnetic core 213 comprises a cylindrical wall 220 which embraces the arm 216 and projects from a head 228 disposed in proximity to the magnet 215. In the embodiment shown in Figure 6 the generator presents a pair of arms 316 which project from the body of the pushbutton 312 to embrace the ferromagnetic core and the winding on opposite sides.

In this case the core 313 presents a lower head 328 in proximity to the magnet 315 and a central shank 313 about which the conductor of the winding 314 is wound.

From the aforegoing it is apparent that the generator of the invention presents numerous advantages, and in particular: - it presents a simple, compact and economical structure requiring only a small number of components for its operation, - it does not require the use of a return spring or similar systems in that the pushbutton returns to its rest position automatically, - the components can be easily assembled,

- it enables the desired electric voltage to be achieved across the winding terminals in that the snap movement of the pushbutton from its rest position to its pressed position is sharp and immediate when the force exceeds a predetermined threshold, as the magnetic pressure between the magnet and ferromagnetic core decades rapidly during their mutual withdrawal,

A wireless transmitter could be incorporated into the generator winding to emit a wireless signal when the pushbutton is pressed. In this manner the generator can perform a wireless pushbutton function, for example in an industrial environment to form a limit switch, a pushbutton sensor or the like. in the embodiment shown in Figure 7 the pushbutton 412 presents an upper flat portion 427 intended to be pressed by the user, and two inwardly projecting flanges 418 provided with holes to receive a pin 428 for hinging it to the generator casing, The pushbutton also comprises an arm 419 projecting from the upper flat portion 427 towards the generator interior from the opposite end to the flanges 418,

When assembly is complete (see Figures 7 and 8) the arm 419 rests with its end against a movable portion 416 of ferromagnetic material, The core 413 comprises a circular upper wall 441 and a cylindrical side wall 440, With the generator assembled, the side wall 440 embraces the winding 414, which remains contained within the cylindrical cavity 420 of the core 413.

The core 413 comprises a pair of eyelets 421 to receive the hinge pin 428. The electrical winding 414 is annular in shape and presents an inner cavity 422 housing the magnet 415.

The magnet 415 is cylindrical to mate with a central cavity 422 for example by forcing, and presents two poles disposed in sequence along an axial direction of the winding 414.

The movable portion 416 is of L-shape, comprising a wall 442 substantially parallel to the axis of the winding 414 and positioned laterally to this latter.

At the top of the waif 442 there is an external hole 423 to receive the hinge pin 428, at the level of which the L-shaped portion remains interposed between the flange 418 and the eyelets 421.

The movable portion 16 also comprises a positionable wall 429 which extends below the winding, until it projects from the side opposite the vertical wall 442. The end of the wall 429, at least during pushbutton pressing, rests against the arm 419 within the pushbutton.

The casing 417 is of upperly open parallelepiped box form and comprises a lower wall 434, two side walls 432 and 433, and two longitudinal side walls 430, 431. The side walls 430, 433 form a cavity 424 which receives the winding 414, the core 413 and the L-shaped movable portion 418,

The longitudinal side walls 430 and 431 have a concavity 425 forming a seat to receive opposing sides of the core, such that this remains rigid within the casing during normal generator operation.

The casing 417 also comprises two flanges 426 at its opposing iongitudinal ends, for fixing the pushbutton generator for example to a wall. The core 413 and the movable portion 416 form an iron magnetic circuit which is exposed to the magnetic flux generated by the permanent magnet 415,

The generator of this embodiment operates in the following manner. When at rest the pushbutton is in the raised position with the upper flat portion 427 substantially parallel to the base of the casing 417.

The movable iron portion 416 is virtually in contact with the magnet 415, thθ lower face of the winding 414 and also the lower edge of the cylindrical side wail of the core 413. The lower wall 429 of the L-shaped element rests against the arm 419 of the pushbutton 412,

The magnetic attraction force between the magnet 415 and the ferromagnetic movable portion 416 together with the fact that the pushbutton 412 rests against the upper edge of the casing 417 means that the pushbutton 412 is maintained securely in the raised rest position as shown in Figure 7.

When the pushbutton 412 is pressed by the user, with a force exceeding a predetermined threshold depending on the magnetic attraction force between the magnet 415 and the movable portion 416, the pushbutton 412 moves into the lowered position shown in Figure 8. The arm 419 pushes against the lower wall 429 of the portion 416 to cause its withdrawal from the magnet 415 against the force of attraction.

The core 413, the winding 414 and the magnet 415 remain rigid with the casing 417 by virtue of their engagement in the casing seats 425.

The movement of the portion 416 takes place with a sharp snap action, due to the rapid decay of the magnetic attraction force as the magnet

415 separates. The magnetic circuit changes configuration and opens. The magπetic flux passing through the winding 414 hence varies so that an electric voltage is generated across the winding terminals.

The core 413 forms a limit stop for the descent of the pushbutton 412.

When the pressing action on the pushbutton 412 ceases, the magnetic attraction force between the magnet 415 and the wall 429 returns the portion

416 upwards, this also urging the pushbutton 412 by virtue of resting against arm 419.

The generator hence returns to its starting position of Figure 8.

The magnetic flux which cuts the winding also varies during the resetting of the pushbutton, to return to its maximum value, so generating a new voltage pulse.

Alternatively the magnet could a!so not be fixed rigidly to the winding and to the casing, but could be movable rigid with the movable portion 416 of the magnetic circuit. In a further embodiment not shown in the drawings, a polarized magnet is used in radial direction instead of in the axial one.