WO1993021684A1

WO1993021684A1 - A circuit for controlling a vibration pump, for example for drink dispensing machines

Info

Publication number: WO1993021684A1
Application number: PCT/EP1993/000843
Authority: WO
Inventors: Edoardo Macchi
Original assignee: Luigi Lavazza SpA
Current assignee: Luigi Lavazza SpA
Priority date: 1992-04-09
Filing date: 1993-04-06
Publication date: 1993-10-28
Anticipated expiration: 1994-10-09
Also published as: ITTO920326A0; ITTO920326A1; IT1259532B

Abstract

A vibration pump (1) arranged to be supplied with mains voltage is controlled from a DC voltage via an oscillator and a power circuit operating with a power transistor such as an HEX-FET (17). Preferred applications are in apparatus for the preparation of drinks such as coffee, tea and chocolate.

Description

A CIRCUIT FOR CONTROLLING A VIBRATION POMP. FOR EXAMPLE FOR DRINK DISPENSING MACHINES

The present invention relates in general to electronic control circuits and specifically to an electronic circuit for controlling a vibration pump.

Pumps of this type are utilised in various branches of the art and, in particular, in machines for dispensing drinks, for example coffee, tea, chocolate etc.

Such pumps are normally made in such a way as to be able to operate from an alternating supply, usually about 220 volts (mains voltage) .

In some applications, however, a requirement arises to make such pumps operate with a DC supply, for example a DC voltage of 12 or 24 volts.

This requirement arises, for example, when it is desired to mount a vibration pump on a vehicle such as a bus or a railway carriage the electrical equipment of which is supplied by 24 volts DC.

At least in principle this problem could be resolved by utilising a converter circuit of generally known type, operable to convert the DC supply to an alternating supply with corresponding voltage increase. This, however, is rather complex from the point of view of the circuit, above all in applications in which the cost factor has a determining role.

The present invention therefore seeks to provide means allowing a vibration pump to be supplied, in an almost direct manner, from a DC supply, above all a DC supply of low voltage (12, 24 or 48 volts) .

According to the present invention this object is achieved by a circuit having the characteristics set out in a specific manner in the claims which follow.

In essence, the present invention, in its preferred embodiment, is based on the idea of allowing the operation of a normal vibration pump by supplying it with DC through an oscillator and a power supply circuit operating with HEX-FET, that is to say with a transistor able to deliver very high currents.

The invention will now be described, purely by way of non-limitative example, with reference to the attached drawings, in which:

Figure 1 illustrates, in the form of a block diagram, the general configuration of apparatus incorporating a circuit according to the invention; and Figure 2 illustrates in more detail the structure of the circuit according to the invention.

The Figure 1 diagram reproduces, purely by way of example, the structure of the control circuit for an electric vibration pump 1 intended to allow delivery of water under pressure into apparatus for preparing and dispensing drinks such as coffee, tea or chocolate. As already mentioned, however, this possible application is ^• not to be interpreted in a limitative sense.

The pump 1 is controlled through a power supply circuit 2 the structure of which will be illustrated better with reference to the diagram of Figure 2. The circuit 2 is in turn controlled by an oscillator circuit 3 subject to control logic 4 (for example a micro processor) .

Various input/output lines lead to the micro processor 4 and are connected to various other circuit modules.

In particular, the reference numeral 5 indicates a voltage stabiliser circuit, in turn connected to the general supply source of the device, represented by a battery 6 able to deliver a voltage of 12, 24 or 48 volts (depending on the type of vehicle on which the device is mounted) . Usually the circuit 5 and the battery 6 are also connected to a module 7 for controlling the temperature to which the water utilised for the preparation of the drinks is heated: this water is received in a boiler (not illustrated) which has an associated heating resistor 8 controlled by the circuit 7.

The reference numeral 9 indicates a sensor connected to a water level indicating float in the boiler, whilst the reference numeral 10 indicates an operating push button intended to be actuated by the user to stop delivery of the drink once it has reached the desired level.

A further sensor switch 11 is sensitive to the introduction into the machine of a capsule containing powder material for the preparation of the drink.

Alternatively the switch 11 could be simply constituted by another actuating switch intended to be activated by the utiliser.

Finally, the reference numeral 12 indicates a solenoid valve for controlling the delivery of water, whilst the reference 13 indicates a warning lamp for indicating the level of water, intended in particular to indicate when this level falls below a minimum acceptable value. The general operating criteria for the machine, and therefore for the control logic 4 and elements 5 to 13 associated with it, are widely known per se and do not need to be illustrated in detail here: in addition they are not relevant for the purpose of understanding the invention.

In this respect it is sufficient to recall that upon the occurrence of given events, or sequences of events, the logic 4 commands activation of the pump 1: to this end the logic 4, via the resistance 107, will pull the base of the NPN transistor 105 down to earth, which transistor, no longer being in conduction, will allow pulses generated by the oscillator stage 3 to reach the bases of the transistors 14a and 14b via the resistor 106.

The oscillator circuit 3 is constituted by a stage comprising two bistable circuits such as two Schmitt triggers 100a, 100b (each constituted, for example, by one sixth of a CMOS integrated circuit 40106) connected in cascade as illustrated in Figure 2, with the output of the downstream trigger 100b (constituting the output of the oscillator) fed back to the input of the upstream trigger 100a through a capacitor 101 (typical value 0.1 μF) . To the output of the upstream trigger 100a, which controls the input of the downstream trigger 100b, is connected a resistor unit 102, 103 connected to the terminal of the capacitor 101 opposite that connected to the output of the downstream trigger 100b so as to form an RC unit the time constant of which regulates the feedback action to the input of the oscillator 3 so as to cause selective variation of the oscillation frequency.

For example the resistor 102 can have a resistance value of 82 K Ohm, and the resistor 103 may be a multiturn 50 K Ohm potentiometer.

By acting on the potentiometer 103 it is thus possible selectively to vary the frequency of oscillation of the circuit 3, which, as can be seen, can be activated by a control pulse applied by the logic 4 to the enabling input 104.

The oscillator 3 is able to produce at its output a square wave signal with a frequency of the order of, for example, 50-100 Hz adjustable (by acting on the potentiometer 103) to achieve a precise adaptation to the mechanical characteristics of the pump 1 so as to obtain the maximum output pressure (10-13 atmospheres) . In this connection it will be noted that, for the purpose of performing the invention, it is not in any way necessary that the oscillation frequency of the circuit 3 , and therefore the control frequency of the power circuit 2 be a frequency corresponding to the mains frequency (typically 50 Hz) for which the pump 1 has been originally arranged to operate. The pump 1 is in fact a normal vibration pump intended to be supplied by connection to the electrical mains.

When the transistor 105 is not conducting, the power circuit 2 receives, via the resistor 106 (10 K Ohm) , the output signal from the oscillator circuit 3 at its input stage comprising the two transistors 14a and 14b connected in a complementary symmetrical arrangement (push-pull) .

In particular the transistor 14a comprises an NPN transistor the collector of which is connected to the DC voltage. This latter is constituted usually by the battery voltage Vb (when this latter is 12 volts) or the battery voltage stepped down by a voltage divider or the like, if the battery voltage is of higher value (24-48 volts). The emitter of the transistor 14a is connected to the emitter of the transistor 14b, which is a PNP type transistor the collector of which is connected to the circuit earth.

The output signal from the oscillator is passed to the bases of the two transistors 14a, 14b which are connected together. Respective diodes 15a and 15b serve as protection for the two transistors 14a, 14b.

The signal present at the emitters of the two transistors 14a, 14b (which emitters are connected together) is transferred through a power resistor 16 (for example a % watt resistor with a resistance value of the order of 10 Ohm) to the gate electrode of the component 17 having HEX FET characteristics the source electrode of which is connected to earth M, whilst the drain electrode is connected to one of the terminals of the pump 1, the

,ι other terminal of which is connected directly to the battery voltage Vb (12, 24 or 48 volts).

The component 17 is usually constituted by an N-channel power FET of the enhancement mode type such as, for example, IRFP150 able to deliver currents of the order of 40 amps.

Between the gate and source of the field effect transistor 17 there is present a polarisation resistor 18 (typical value 10 K Ohm), whilst a diode 19 of FAST type, for example a By 329, is connected with its anode to the source of the transistor 17 and with its cathode to the drain of the same component. The FAST diode 19 protects the transistor 17 from strong reverse currents due to inductive load. In parallel with the diode 19 there is connected a capacitor 20 which, in the example, is0.47 μF having a working voltage of 250 volts and which acts as a filter.

The arrangement described is such that the transistor 17 is alternatively conductive and non-conductive (that is to say switched off and saturated) by the output signal from the input stage constituted by the two transistors 14a, 14b.

In this way the transistor 17 behaves as a sort of switch connected in series with the pump 1 between the battery voltage V and earth with the capacity of selectively allowing currents of high intensity through the pump 1, according to whether the transistor 17 itself is in conduction or switched off.

The voltage control arrangement normally provided for the pump 1 (excitation voltages of high value typically the 220 volts of the mains network, or the alternating 24 volts possibly taken from a transformer with 220 volt primary winding and a 24 volt secondary winding, both of adequate power) is on the other hand replaced in the arrangement according to invention with a DC control (high current values by comparison with moderate voltage values, such as the DC voltage values of a battery) .

All this is achieved without requiring any variation or modification of the structure of the pump and with the further advantage, for the producer and for the user, of not having to arrange to have different replacement parts for pumps intended to be used with low voltage DC supplies.

Naturally, the principle of the invention remaining the same, the details of constructions and embodiments can be widely varied with respect to what has been described and illustrated without by this departing from the present invention. This is relevant in particular as far as it concerns the possibility of replacing the HEX-FET transistor 17 described above with a functionally equivalent electronic switch.

Claims

1. A circuit for controlling, from a DC electrical supply, a vibration pump designed to be supplied from the alternating electric mains network, characterised by the fact that it comprises: an oscillator (3)fargenerating an oscillating electric signal and an electronic switch (17) or commutation of high currents, controlled by said oscillator (3) and .able to be alternatively open and closed by said oscillating electrical signal for selectively controlling the passage of current through said vibration pump (1) ; said vibration pump (1) being connected to said DC supply source.

2. A circuit according to Claim 1, characterised in that said electronic switch is a power transistor (17).

3. A circuit according to Claim 2, characterised in that said transistor is a field-effector transistor, preferable a HEX-FET.

4. A circuit according to Claim 1 or Claim 2, characterised in that said electronic switch (17) is controlled by said oscillator (3) via a stage (14a, 14b) having complementary symmetry.

5. A circuit according to any preceding Claim, characterised in that said electronic switch (7) is connected in series to said vibration pump (1) .

6. A circuit according to any preceding Claim, characterised in that said oscillator (3) includes at least two bistable circuits (100a, 100b) connected in cascade with one another in a general feedback arrangement.

7. A circuit according to Claim 1 or Claim 6, characterised in that it includes means (103) for selectively varying the frequency of said oscillating electric signal.

8. A circuit according to Claim 6 and Claim 7, characterised in that said bistable circuits (100a, 100b) are fed back by means of a circuit, preferably an RC circuit (101 to 103) , with a selectively variable time constant.

9. A circuit according to Claim 3 and Claim 5, characterised in that said field-effect transistor (17) is connected by one of the source (S) and drain to earth (M) of the circuit and by the other of said source and drain to one of the terminals of said pump (1) , the other terminal of said pump being connectable to said DC supply source (Vb) .