TECHNICAL FIELD

The present invention relates to a concrete vibrator system, and in particular to a portable immersion concrete vibrator.

BACKGROUND ART

Portable immersion concrete vibrators are typically used by construction site workers for deaerating a mass of liquid concrete within a formwork so as to accelerate concrete hardening. An immersion concrete vibrator normally comprises a motorized vibrating body adapted to be immersed in a mass of liquid concrete to transmit vibrations to the concrete, and a driving circuit for actuating the motor of the vibrating body. The vibrating body comprises an AC motor, an eccentric mass mounted to the rotating shaft of the motor and a watertight rigid case which houses the motor and the eccentric mass. The driving circuit is normally housed in a box, is electrically powerable by means of the normal electric mains, and is connected to the motor of the vibrating body by means of an electric wire.

The known immersion vibrators essentially differentiate due to the motor type of the vibrating body and to the type of driving circuit. In a first type of immersion vibrator, the motor of the vibrating body is a three-phase 50 V, 200 Hz motor and the driving circuit comprises a mono-phase 230 V, 50 Hz AC motor, or three-phase 400 V, 50 Hz AC motor, and a permanent magnet converter, which is coupled to such an AC motor and generates a three-phase alternating voltage at 50 V, 200 Hz to be supplied to the vibrating body. This type of immersion vibrator is safe from the electric point of view, because the vibrating body works with 50V voltage (low voltage) , but is rather heavy because the driving circuit comprises an AC motor and a permanent magnet converter. The weight of this type of immersion vibrator may indeed exceed 20 kg.

In a second type of immersion vibrator, the motor of the vibrating body is a three-phase 230 V, 200 Hz motor and the driving circuit comprises an inverter for converting a mono-phase 230 V, 50 Hz voltage into a three-phase 230 V, 200 Hz voltage to be supplied to the vibrating body. This type of immersion vibrator is lighter than that described above but is less safe because the vibrating body works at 230 V.

In a third type of immersion vibrator, the motor of the vibrating body is a three-phase 50 V, 200 Hz motor and the driving circuit comprises an inverter for converting a mono-phase 230 V, 50 Hz voltage into a three-phase 230 V, 200 Hz voltage, and a three-phase transformer coupled to the output of the inverter to decrease the voltage to 50 V. This type of vibrator is rather heavy and not very efficient due to the presence of the transformer, which is heavy and generates losses, and is however not very safe because part of the driving circuit, i.e. the coupling between inverter and transformer, works at a relatively high voltage (230 V) . DISCLOSURE OF INVENTION

It is the object of the present invention to provide a concrete vibrator system, and in particular a portable immersion concrete vibrator, which is free from the above-described drawbacks while being easy and cost- effective to be provided.

In accordance with the present invention, a concrete vibrator system is provided as defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding the present invention, a preferred embodiment will now be described merely by way of non-limiting example, and with reference to the accompanying drawings, in which:

figure 1 is a block chart of the concrete vibrator system provided according to the dictates of the present invention; and

- figure 2 shows a particular embodiment of the concrete vibrator system in figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION

In figure 1, numeral 1 generally indicates, as a whole, a concrete vibrator system, which comprises at least one motorized vibrating body 2 for transmitting vibrations to a mass of liquid concrete, and at least one driving circuit 3, designed to actuate the motor of vibrating body 2. The driving circuit 3 is powerable by the electric mains 4 and is connected, with its output, to the motor of vibrating body 2 by means of a switch 5 manually operable by an operator. In the embodiment described below, the electric mains 4 is mono-phase and the electric mains voltage Vs has an amplitude of 230 V and oscillates at a frequency of 50 Hz. Alternatively, the driving circuit 3, and thus the vibrator system 1 in general, is powerable by another AC electric power source, e.g. an AC electric generator actuated by a combustion engine.

The vibrator body 2 comprises a three-phase AC motor 6, which works at an AC voltage Vac having an amplitude lower than that of the electric mains voltage Vs and oscillating at a predetermined frequency higher than that of the electric mains voltage Vs, and an eccentric mass 7 mounted to the rotating shaft of motor 6. In particular, the voltage Vac has an amplitude VM1 lower than 50 V and oscillates at a frequency F essentially between 180 and 240 Hz. For example, the voltage amplitude V 1 is between 42 and 48 V. Preferably, the frequency FM is substantially equal to 200 Hz.

The driving circuit 3 comprises at least one switching power supply 8, which receives the electric mains voltage Vs and provides a DC voltage Vdc having an amplitude lower than that of the electric mains voltage Vs, and at least one DC/AC inverter 9, which is connected between switching power supply 8 and motor 6, in particular between switching power supply 8 and switch 5, to transform voltage Vdc into voltage Vac. Voltage Vdc may generally have an amplitude VM2 different from the amplitude VMl of voltage Vac. Advantageously, the voltage amplitude VM2 substantially coincides with the voltage amplitude VMl.

The switching power supply 8 is of the resonating type, which is known per se and has the following advantages, the generated power being equal, as compared to a traditional rectifying circuit or a traditional power supply:

- smaller dimensions and weight;

- greater efficiency;

- less produced heat; and

- higher electric insulation towards the outside. The switching power supply 8 comprises a particular type of transformer working at frequencies of tens or hundreds of thousands Hertz, instead of 50 Hz of the electric -mains— voitage Vs. he— core of this type of transformer is made of Ferrite, which is a material consisting of glued metal powders, while the core of traditional transformers is made of iron foils, which produce, at high frequencies, considerable energy loss. The switching power supply 8 can accept a wide range of electric mains voltages Vs at its input, e.g. the mains voltage at 230 V, 50 Hz (European electric mains) or the mains voltage at 115 V, 60 Hz (United States electric mains), without requiring particular modifications. Furthermore, the switching power supply 8 comprises overload and short-circuit protection systems and filters needed to prevent the high-frequency signal from propagating towards the load or returning towards the electric mains 4.

The DC/AC inverter 9 comprises a plurality of transistors 10, e.g. MOSFET or IGBT, and a microcontroller 11 provided with a clock signal generator 12, e.g. a quartz clock, for generating width- modulated pulse signals, each generated signal being capable of controlling a respective one of said transistor 10.

Driving circuit 3 further comprises a filter 13 designed to allow the driving circuit 3 to satisfy the electromagnetic compatibility requirements (EMC) , such a filter 13 being arranged so as to be in use directly connected to the electric mains 4, and a power factor corrector circuit (PFC) 14, which is connected to the input of the switching power supply 8, between the latter and filter 13, to take the power factor to a value close to 1, and thus to reduce the harmonic distortions produced by the driving circuit 3. Therefore, the switching power supply 8 receives the electric mains voltage Vs which has been already filtered and has a correct power factor.

Figure 2 shows a particular embodiment of the vibrator system 1 according to the invention, consisting of a portable immersion vibrator. According to the embodiment in figure 2, vibrator system 1 comprises a box 15, shown in partially exploded view in figure 2, in which the driving circuit 3 is accommodated and the vibrating body 2 comprises a rigid watertight case 16 of elongated, substantially cylindrical shape, which houses motor 6 and eccentric mass 7 and is adapted to be immersed in a liquid concrete mass to transmit vibrations to the concrete. Box 15 incorporates a handle 17 for facilitating the use and manual transport of vibrator system 1.

Box 15 is substantially parallelepiped-shaped and has, at the two greater faces of the parallelepiped, two respective flat finned dissipators 18 and 19 arranged with their respective finned sides outside box 15. The driving circuit 3 is implemented on two printed circuit boards 20 and 21. The printed circuit board 20 comprises the switching power supply 8 and the power factor corrector circuit 14 (not shown) and is mounted to the internal side of dissipator 18, and the printed circuit board 21 comprises DC/AC inverter 8 and filter 13 and is mounted to the internal side of the other dissipater 19. Box 15 comprises a power wire 22, which is connected to the input of the activation circuit 3, in particular to the input of filter 13, and protrudes from a smaller face 23 of box 15, ending with a mono-phase industrial plug 24 which can be engaged in a corresponding mono-phase industrial socket (not shown) of the electric mains 4. Box 15 further comprises a three-phase industrial socket 25, which is arranged on a smaller face 26 opposite face 23 and is connected to the output of the activation circuit 15, in particular to the output of the DC/AC inverter 9.

The rigid case 16 has one end 16a thereof structurally coupled to the external box 27 of switch 5 by means of a rubber sleeve 28, in which there is a wire (not shown) for electrically connecting a terminal of switch 5 to motor 6. The other terminal of switch 5 is connected, by means of an electric wire 29, to an industrial three-phase plug which is engaged in the three-phase socket 25.

According to a further embodiment (not shown) of the present invention, vibrating system 1 comprises one or more vibrating bodies 2, each comprising a respective ^" Tigid case which houses therein the AC motor 6 and the eccentric mass 7, and is adapted to be rigidly mounted to a wall of a concrete formwork for transmitting vibrations to the liquid concrete mass contained inside the formwork. Each vibrating body 2 is connected to the activation circuit 3 by means of a respective switch 5. According to the number of vibrating bodies 2, and thus according to the required mechanical power, the activation circuit 3 may comprise one or more switching power supplies 8 and one or more DC/AC inverters.

The main advantage of the above-described concrete vibrator system is that it is safe while being light and very efficient due to the cascade arrangement between switching power supply and DC/AC inverter 9. Such an advantage is very evident in the embodiment consisting of a portable immersion vibrator, the weight of which does not exceed 6 kg. However, in any of the above- described embodiments, the efficiency of the concrete vibrator system according to the invention is between 93% and 95%.