Machine for producing and dispensing liquid or semiliquid foodstuffs

1. A machine for producing and dispensing a liquid or semiliquid product for use as a foodstuff, comprising:

a holding vat for a liquid base product;

a treatment circuit for said liquid base product, in order to obtain a liquid or semiliquid foodstuff, said treatment circuit comprising at least one heat-adjustment system for adjusting at least one value associated with a temperature of at least one chosen from said base product, an intermediate product and a finished product;

a dispensing mechanism for distributing said foodstuff;

wherein said heat-adjustment system comprises:

a thermal circuit within which a thermal fluid circulates, and including a compressor, a condenser, an electronic expansion valve, and an evaporator, an outlet of the compressor being fluidly connected to an inlet of the condenser, an outlet of the condenser being fluidly connected to an inlet of the evaporator, an outlet of the evaporator being fluidly connected to an inlet of the compressor and said electronic expansion valve being interposed between said condenser and evaporator;

a control unit acting on said electronic expansion valve for adjusting a passage section of the electronic expansion valve through an electronic command signal (S), said control unit being configured for:

determining a main parameter (SH) representative of an actual instantaneous overheating of the thermal fluid coming out of the evaporator, wherein said main parameter (SH)=(Tout)−(Tsat), where:

(Tout) is a temperature of the fluid coming out of the evaporator, the temperature of the fluid taken between the outlet of the evaporator and the inlet of the compressor;

(Tsat) is a saturation temperature of the fluid coming out of the evaporator; wherein (Tsat) is determined as a function of a pressure (Pout) of the fluid coming out of said evaporator, the pressure (Pout) of the fluid also taken between the outlet of the evaporator and the inlet of the compressor;

determining a target reference parameter (SHset) for said overheating, a value thereof being a value that the instantaneous overheating should take to enable the foodstuff to at least one chosen from, reach a desired temperature and keep a desired temperature, said target reference parameter (SHset) being determined as a function of a predetermined value (SHmin), and of an auxiliary value (DT) calculated depending on a variation in time of the temperature (Tout) of the fluid coming out of the evaporator and of the saturation temperature (Tsat) of the fluid coming out of the evaporator such that the auxiliary value (DT) is calculated based on both 1) instantaneous values of (Tout) and (Tsat) taken at a current time and 2) values of (Tout) and (Tsat) taken at previous times;

generating said electric command signal (S) as a function of a comparison between said main parameter (SH) and target reference parameter (SHset).

2. The machine of claim 1 , wherein said treatment circuit comprises a cooling and mixing unit equipped with a whipping device, said evaporator being thermally associated with said whipping device for adjusting the temperature of the foodstuff present in said whipping device.

3. The machine of claim 1 , wherein said heat-adjustment system further comprises a first sensor adapted to detect a parameter representative of the pressure (Pout) of the fluid coming out of said evaporator.

4. The machine of claim 1 , wherein said heat-adjustment system further comprises a second sensor adapted to detect a parameter representative of the temperature (Tout) of the fluid coming out of said evaporator.

5. The machine of claim 1 , wherein said auxiliary value (DT) is determined as a function of a variation in time of an average between the temperature (Tout) of the fluid coming out of the evaporator and the saturation temperature (Tsat) of the fluid coming out of the evaporator.

6. The machine of claim 1 , wherein said auxiliary value (DT) is determined as a function of a derivative in respect of time of a parameter depending on the temperature (Tout) of the fluid coming out of the evaporator and on the saturation temperature (Tsat) of the fluid coming out of the evaporator.

7. The machine of claim 5 , wherein said auxiliary value (DT) is determined as a function of a derivative in respect of time of an average between the temperature (Tout) of the fluid coming out of the evaporator and the saturation temperature (Tsat) of the fluid coming out of the evaporator.

8. The machine of claim 1 , wherein said predetermined value (SHmin) is a constant value fixed during the starting setting of the heat-adjustment system.

9. The machine of claim 1 , wherein said target reference parameter (SHset) is determined as a function of a sum between said predetermined value (SHmin) and auxiliary value (DT).

10. The machine of claim 1 , wherein said control unit is configured for applying a PID control technique to an error defined by a difference between said main parameter (SH) and target reference parameter (SHset), for generating the electric command signal (S).

11. The machine of claim 10 , wherein the PID control technique calculates the proportional term P as a product of the proportional term P and of an absolute value thereof |P| to obtain a value equal to a square of the value of term P and also having a sign of the term P.

12. The machine of claim 4 , wherein said second sensor comprises at least one chosen from a resistive temperature sensor, and a thermocouple.

13. The machine of claim 1 , wherein said electronic valve comprises an adjustable closure member and an electromechanical actuator for adjusting said closure member, said command signal (S) for controlling said electromechanical actuator.

14. The machine of claim 1 , wherein said auxiliary value (DT) is determined as a function of a variation in time of a mean of a plurality of temperatures (Tout) of the fluid coming out of the evaporator and saturation temperatures (Tsat) of the fluid coming out of the evaporator taken at a sampling frequency, and at each sampling instant of these temperatures, increasing the target reference parameter (SHset) by a factor proportional to a derivative of a moving average of the mean of (Tsat) and (Tout).

15. The machine of claim 1 , wherein the control unit generates said electric command signal (S) for limiting opening of the passage section of the electronic expansion valve to a predetermined maximum value and overrides the predetermined maximum value only if the main parameter (SH) falls below a predetermined value.

16. The machine of claim 1 , wherein the saturation temperature (Tsat) is determined as the function of the pressure (Pout) via a prestored correspondence table in which each pressure (Pout) value is associated with a corresponding saturation temperature (Tsat) table.

17. The machine of claim 16 , wherein the prestored correspondence table is derived from a saturation curve of the thermal fluid used in the thermal circuit.