The present invention relates in general to hot beverage vending machines, and in particular to electronic control of a dual-stage water heater for use in hot beverage vending machines, such as coffee-based beverages, e.g. espresso coffee (ES), instant coffee (INST) and/or fresh brew coffee (FB).
Hot beverage vending machines are known to be equipped with single-stage water heaters, i.e., with a single water tank and a single water heater, usually of the electric resistance type, placed inside the water tank, or with dual-heating stage water heaters, i.e., with two series-connected water tanks arranged one inside the other, and two water heaters associated with the two water tanks.
An example of a dual-stage water heater is described in DE 3218442 or US 2004/0079749. In these examples, the water heater comprises a main water tank provided with a first heater operable to heat up and keep water at a first predetermined stand-by temperature, and a smaller secondary water tank, arranged inside the main tank, thermally insulated therefrom, and provided with a second heater operable to heat up and keep water at a second, predetermined stand-by temperature higher than the first temperature.
Another example of a dual-stage water heater for hot beverage vending machines is described in CH 367610, wherein the second water heater is operated only when steam it to be produced. In this example, a valve is provided which, responsive to pressure increase in the secondary tank, interrupts the fluidic communication between the two water tanks so that only the amount of water contained in the secondary tank is transformed into steam.
In the above examples, the two water heaters are of a storage type, i.e., in which a given amount of water is stored in a water tank and heated up and kept at the desired temperature, and when the water heater is required to dispense a given amount of hot water to prepare a beverage, the withdrawn water is replenished with fresh water and the water in the water tank is then heated up and brought back to the desired temperature.
The Applicant has found that single-stage or dual-stage storage water heaters described in the above documents have numerous drawbacks, the main ones of which are:
A dual-stage water heater for hot beverage vending machines capable of overcoming the above-mentioned drawbacks is described in WO 2014/027310 A1, in the name of the Applicant, in which the first heating stage is of the water storage type, while the second heating stage is of the continuous flow type, i.e. in which water is heated to the desired temperature while flowing through the second heating stage when a beverage is selected, i.e. only when water is withdrawn to meet the water demand necessary to prepare a beverage.
The object of the present invention is to provide an electronic control system for a dual-stage water heater of the type described in WO 2014/027310 A1, and capable of efficiently, accurately and reliably controlling the temperature of the water supplied by the dual-stage water heater.
According to the present invention, an electronic control system for a dual-stage water heater in a hot beverage vending machine, and a dual-stage water heater provided with such an electronic control system are provided, as claimed in the appended claims.
The present invention will now be described in detail with reference to the attached figures to enable a person skilled in the art to make and use it. Various modifications to the described embodiments will be immediately appreciable to a person skilled in the art and the general principles described may be applied to other embodiments and applications while remaining within the scope of the present invention, as defined by the appended claims. The present invention should not therefore be considered to be limited to the embodiments described and shown, but given a broader scope of protection according to the features described and claimed.
The water heater 1 has a single cold water inlet 3 fluidly connectable to a hydraulic circuit 5 configured to supply cold water (at room temperature) to the cold water inlet 3, and a single hot water outlet 4 fluidly connectable to a beverage production unit (not shown).
The hydraulic circuit 5 comprises a water pump 6 with an intake fluidly connected to a cold water source (not shown) through a suitable water filter 7, and a supply fluidly connected to the cold water inlet 3 of the water heater 1 through a pressure control valve 8 calibrated so as to recirculate towards the intake of the water pump 6, through a bypass branch 9 and a T-connection 10, the water delivered by the water pump 6, when water pressure in the water heater 1 exceeds a maximum pressure.
In one embodiment, the hydraulic circuit 5 is also conveniently configured to carry out two additional functions of mixing hot water dispensed by the water heater 1 with cold water to cause a rapid cooling of hot water dispensed by the water heater 1, and of bypassing the water heater 1. In particular, to accomplish this, the hydraulic circuit 5 is configured to cause cold water supplied to the water heater 1 to be partializable to supply a part to the cold water inlet 3 and a part towards the hot water outlet 4 to mix it with hot water and cause, when needed, as said, a rapid cooling of hot water, as described in more detail below.
To achieve these additional functions, the hydraulic circuit 5 comprises a T-junction 11 having an I/O port fluidly connectable to the pressure control valve 8, an I/O port fluidly connected to the cold water inlet 3 of the water heater 1 through a first solenoid valve EV1 12, and an I/O port fluidly connected to the cold water inlet 13 of the water mixer 14 through a second solenoid valve EV2 15 and a bypass branch 16. The water mixer 14 has also a hot water inlet 17 fluidly connected to the hot water outlet 4 of the water heater 1 and a mixed water outlet 18.
Under normal operating conditions, the first solenoid valve EV1 12 is controlled to be open to cause cold water to be supplied to the cold water inlet 3 of the water heater 1. The second solenoid valve EV2 15 is instead controlled by appropriate PWM modulation to adjust the opening period and, consequently, the cooling of the water supplied by the water heater 1.
In an alternative embodiment, the hydraulic circuit 5 is configured to carry out only the function of supplying cold water to the cold water inlet 3 of the water heater 1, and not also the two additional functions of mixing the hot water dispensed by the water heater 1 with cold water and of bypassimg the water heater 1.
In one embodiment, the water heater 1 is conveniently of the type described and shown in WO 2014/027310 A1, in the name of the Applicant, and the content of which is to be considered incorporated herein in its entirety, and is schematically shown in
In particular, the water heater 1, which will be described below limited only to the features necessary to understand the present invention, comprises:
The water boiler 20 comprises:
In the embodiment shown in
The water booster 21 comprises:
In the example shown in
In a different embodiment not shown, the external water tank 22 may be in the form of a box-shaped body formed of a cup-shaped body closed by a lid, while the internal body may be again be in the form of a generally cylindrical tubular body, but arranged in the external water tank 22 transversely to the longitudinal axis thereof.
In the embodiment shown in
In the embodiment shown in
The water heater 1 further comprises an electronic control system 30 comprising:
In the embodiment shown in
Conveniently, the first temperature sensor 33 is arranged to measure water temperature at an end of the water boiler 20 opposite the cold water inlet 3 of the water heater 1, in the example shown in
In a different embodiment not shown, the sensory system 31 may comprise only the first and third temperature sensors 33 and 35 and not also the second temperature sensor 34, so as to measure only water temperatures in the water boiler 20 and at the hot water outlet 4 of the water heater 1.
In a further embodiment not shown, the sensory system 31 may comprise only the first and second temperature sensors 33 and 34 and not also the third temperature sensor 35, so as to measure only water temperatures in the water boiler 20 and in the water booster 21. In this embodiment, the second temperature sensor 34 may conveniently be arranged at the top of the water booster 21, i.e., at the water outlet of the water booster 21, so as to measure a water temperature very close to, and thus indicative of, the water temperature at the hot water outlet 4.
In the embodiment shown in
The aim of the control is to control water temperature in the water boiler 20 and in the water booster 21 such that they follow as closely as possible the following two reference temperatures:
The electronic control unit 32 is programmed to achieve this specification by operating based on a mathematical model of the water heater 1 as a whole and of the first and second electric heaters 27, 28, and on measured water temperatures Text_m, Tbooster_m and Tout_m.
The electronic control unit 32 is programmed to compare the measured water temperatures Text_m and Tout_m with the reference water temperatures Text_d and Tout_d, so as to compute error temperatures based on which control signals are generated for the three electrical resistors 27, 28 and 29, and in particular:
R_Boiler_Low: electric control signal for the lower resistance R1 of the water boiler 20,
R_Boiler_Hi: electrical control signal for the higher resistance R2 of the water boiler 20,
R_Booster: electrical control signal for the resistance R3 of the water booster 21, and
EV_bypass(t): electrical control signal for the solenoid valve EV2 15.
In the embodiment in which the third temperature sensor 35 is not provided to measure water temperature Tout_m at the hot water outlet 4 of the water heater 1, this can be estimated based on the measured water temperature TBoost_m in the water booster 21 measured by the second temperature sensor 34 conveniently arranged at the water outlet of the water booster 21.
However, reference water temperature Tbooster_d is not a desired value stored by an operator in the electronic control unit 32 or by a higher control, but is a value computed by a Planner described below.
The meanings of the input and output variables of the blocks shown in
1. Water Boiler Control
The water boiler control 36 operates as shown in the functional block diagram shown in
2. Planner and Water Booster Control
The water booster control 37 operates as shown in the functional block diagram shown in
The water booster control 37 is more complex than the water boiler control 36 and is based on:
all of which concur to provide the Energy Manager 38 with an electrical power demand PW-R3 for the resistance of R3 the water booster 21.
Based on the measured water temperature TBoost_m in the water booster 21 and the desired water temperature TBoost_d computed by the planner 40, the water temperature error eTbooster=Tbooster_d-Tbooster_m is then computed to obtain one of the contributions to the electrical power demand PW-R3 for the resistance R3 of the water booster 21, according to the proportional, derivative and integral terms.
In the embodiment in which the second temperature sensor 34 to measure the water temperature TBoost_m in the water booster 21 is not provided, this can be estimated based on the water temperature Tout_m measured at the hot water outlet 4 of the water heater 1.
The other contribution to the electrical power demand PW-R3 for the resistance R3 of the water booster 21 is the feedforward component (KFFW) 43, which acts as a proportional factor on the water temperature step from the water temperature in the water boiler 20 to that in the water booster 21.
Also for the water booster 21, as for the water boiler 20, the electric power PwBooster_r requested to the resistance R3 is managed by the energy manager 38, which, based on all the electrical power demands, determines which are to be energized and which don't.
2.1 Planner
The planner 40 operates as shown in the functional block diagram shown in
The planner 40 is designed to compute the time development of the desired water temperature TBoost_d in the water booster 21. Based on the physical response times of the system, the inertias of the resistances and the masses involved, the planner 40 is designed to anticipate the actions to be taken on the desired water temperature TBoost_d in order to try to cancel the inherent thermal system delay. In this way, the water heater 1 may manage the sudden changes in the desired water temperature Tout_d at the delivery point 4 based on the principle of preparing the water heater 1 in advance for the subsequent phase.
For example, for the preparation of a mix beverage, such as cappuccino, if the water booster 21 is not preheated during milk dispensing, the coffee will be cold, because the water booster 21 takes a long time to heat the water therein during the flow phase. Similarly, for the preparation of a mocaccino, to switch from coffee to chocolate dispensing, the water heater 1 must be prepared for early cooling before the end of the coffee dispensing.
The planner 40 acts in response to a beverage selection, first on the preparation phase and then on the dispensing phase. In particular, as shown in
2.1.1 PID Delta Temp
The PID delta temp block temperature contribution 44 is computed only once at the beginning of the preparation phase of each sub-beverage. So, if a beverage comprises three sub-beverages, this temperature contribution is computed three times. This temperature contribution represents the desired water temperature TBoost_d in the water booster 21 to have the desired temperature Tout_d at the delivery point 4. In particular, this temperature contribution represents the temperature delta needed to heat the system downstream of the water boiler 20, between the water booster 21 and the mixed water outlet 18 of the water mixer 14. This contribution is computed based on the following formula:
OutPID=ACT_PHASE.Tout_d-ParTar.th_soglia_pid-Tout_a)*KpOut
wherein:
This temperature contribution is very variable based on the system initial temperature, i.e., on the water temperature measured when the system is cold and is far from the desired water temperature at the delivery point. This temperature contribution is important in order to speed up the heating of the system downstream of the heater, while when the system is already hot, this contribution assumes almost zero, if not negative, values to counteract the inertia to the rise of the water temperature.
2.1.2 Predictive
The predictive temperature contribution 45 represents the desired temperature of a given sub-beverage during delivery thereof. This temperature contribution is necessary in double beverages to take account of the next, beverage and anticipate heating or cooling. This temperature contribution is computed as defined by the following functional code:
wherein:
2.1.3 Phase
The phase temperature contribution 46 represents the heart of the planner 40, because through the beverage preparation or dispensing it is possible to change the behaviour of the water heater, causing it to follow a non-constant temperature development over time.
The temperature contribution is divided for each sub-beverage into five periods:
For each period the temperature contribution depends on some constants defined during a calibration phase (elements of the ParTar structure in Table 3), these contributions are specific for each sub-beverage.
For each individual delivery of a sub-beverage, the five periods are defined as follows, as also schematically shown in
In mix beverages, different deliveries are interspersed with preparation periods, so the diagram shown in
wherein:
3. Energy Manager
The energy manager 38 is designed to manage the following three specifications:
The energy manager 38, a block diagram of which is shown in
The resistance R3 of the water booster 21 takes precedence over the two resistances R1 and R2 of the water boiler 20, and when all the three resistances R1, R2 and R3 must be switched on, the two resistances R1 and R2 of the water boiler 20 are switched on alternately.
To control the flickers, the energy manager 38 is designed to cause the electrical power never to change to an extent higher than a certain threshold power.
A non-deliverable energy recovery system is also implemented. For example, if an electrical resistance is capable of delivering an electrical power of 1000 W, if it is required to deliver 400 W three times, the resistance will be switched on at the third request, delivering 1000 W.
The decisions that is taken by the energy manager 38 may be subdivided, at a conceptual level, into three levels, as shown in the block diagram shown in
3.1 Level 1
Level 1 47 is used to divide the electrical power demand PwRboiler_r into PwR_Low_1 and PwR_High_1 for the two resistances R1 and R2 of the water boiler 20 according to the diagram shown in
The control of the resistance R3 of the water booster 21 uses a different method from that of the resistances R1 and R2 of the water boiler 20: the duty cycle of the PWM used to drive the electrical resistance (set at a frequency of 1.5 Hz) is computed based on the electrical power demand. For recovering the non-delivered electrical power, the integral of the error on the electrical power supplied in the previous step is added to the electrical power required at that moment. The duty-cycle values are fixed at three constant values, so as not to increase the risk of flicker, as defined by the following functional code:
3.2 Level 2
Level 2 48 has the objective of adjusting the deliverable electrical power according to the diagram shown in
The square wave generated by the “Pulse Generator1” block has the following characteristics: amplitude 1, Period 4 s, of which 1 s high and 3 s low.
3.3 Level 3
Level 3 49 aims to avoid electrical power jumps higher than a certain threshold electrical power by controlling the “DeltaP” power delta that the system is required to perform according to the diagram shown in
Number | Date | Country | Kind |
---|---|---|---|
102017000087300 | Jul 2017 | IT | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/IB2018/055642 | 7/27/2018 | WO |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2019/021256 | 1/31/2019 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
20040079749 | Young et al. | Apr 2004 | A1 |
20100066292 | Gottemoller et al. | Mar 2010 | A1 |
Number | Date | Country |
---|---|---|
367610 | Feb 1963 | CH |
103118573 | May 2013 | CN |
3218442 | Nov 1983 | DE |
102014212645 | Dec 2015 | DE |
0577561 | Dec 1996 | EP |
0126521 | Apr 2001 | WO |
2006050856 | May 2006 | WO |
2014027310 | Feb 2014 | WO |
WO 2014027310 | Feb 2014 | WO |
WO 2015016708 | Feb 2015 | WO |
Entry |
---|
Engineering Technology Simulation Learning Videos, Functions of a Closed Loop System, Jul. 7, 2015, Retrieved from the Internet : URL: https://www.youtube.com/watch?v=bEnRRI7XXRs (Year: 2015). |
Machine translation of DE 102014212645 A1 performed on Mar. 9, 2022, Antrag (Year: 2015). |
Machine translation of CN 103118573 A performed on Mar. 9, 2022, Rithener et al. (Year: 2013). |
Machine translation of EP 0577561 B1 performed on Mar. 10, 2022, Luessi (Year: 1993). |
International Search Report and Written Opinion from International Application No. PCT/IB2018/055642 dated Nov. 23, 2018. |
Matlab, “Understanding Control Systems, Part 3: Components of a Feedback Control System”, XP055523703, Retrieved from the Internet: URL:https://www.youtube.com/watch?v=u1pgaJHiiew&index=4&list=PLn8PRpmsu08q8CEOpbZ-cSrMm_WYJfVGd, Nov. 16, 2016 (last accessed Nov. 14, 2018). |
Number | Date | Country | |
---|---|---|---|
20200154940 A1 | May 2020 | US |