CN108937588B - Customized brewing system and method suitable for household Italian coffee machine - Google Patents
Customized brewing system and method suitable for household Italian coffee machine Download PDFInfo
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- CN108937588B CN108937588B CN201810993751.6A CN201810993751A CN108937588B CN 108937588 B CN108937588 B CN 108937588B CN 201810993751 A CN201810993751 A CN 201810993751A CN 108937588 B CN108937588 B CN 108937588B
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- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
- A47J31/00—Apparatus for making beverages
- A47J31/24—Coffee-making apparatus in which hot water is passed through the filter under pressure, i.e. in which the coffee grounds are extracted under pressure
- A47J31/34—Coffee-making apparatus in which hot water is passed through the filter under pressure, i.e. in which the coffee grounds are extracted under pressure with hot water under liquid pressure
- A47J31/36—Coffee-making apparatus in which hot water is passed through the filter under pressure, i.e. in which the coffee grounds are extracted under pressure with hot water under liquid pressure with mechanical pressure-producing means
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- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
- A47J31/00—Apparatus for making beverages
- A47J31/44—Parts or details or accessories of beverage-making apparatus
- A47J31/46—Dispensing spouts, pumps, drain valves or like liquid transporting devices
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- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
- A47J31/00—Apparatus for making beverages
- A47J31/44—Parts or details or accessories of beverage-making apparatus
- A47J31/54—Water boiling vessels in beverage making machines
- A47J31/56—Water boiling vessels in beverage making machines having water-level controls; having temperature controls
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- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
- A47J2201/00—Devices having a modular construction
Abstract
The invention discloses a customized brewing system and a customized brewing method suitable for a household Italian coffee machine, wherein a controller, a sensor, an actuator and a user interaction unit are built on the basis of a common coffee machine to form the customized brewing system; the sensor comprises a weighing module, a thermal resistor, a thermocouple and a pressure gauge; the actuator comprises a solid-state relay and a voltage reduction module; the user interaction unit is used for setting a coffee brewing mode by a user, and the user can select an initial brewing temperature, a temperature gradient mode and a pressure mode and whether to intervene in large flow; the controller drives the actuator through feedforward feedback control based on the model, and regulates and controls brewing temperature, pressure and flow curve according to a coffee brewing mode set by a user; the controller obtains controller parameters through a test modeling and simulation method; on the basis of program control of a common coffee machine, the invention improves the brewing quality of the concentrated coffee by controlling brewing process parameters, so that a user can adjust the taste by himself to meet the brewing requirement.
Description
Technical Field
The invention belongs to the technical field of coffee machines, and particularly relates to a customized brewing system and a customized brewing method suitable for a household Italian coffee machine.
Background
Espresso coffee is a type of coffee that is extracted at high pressure. The hot water flows through the roast and ground coffee under a pressure of about 9bar, and the substances in the coffee powder are brewed into the hot water by mechanical washing and dissolution to form the espresso beverage.
The Italian coffee machine is continuously improved in nearly a century, and the manufacturing process and the mechanical design are mature. Coffee machines generally comprise a water tank, a boiler, a pump, a brewing head, a powder bowl, etc. The cold water in the water tank is pumped into the boiler under the action of the pump to be heated. When the coffee machine works, the pump is started, and hot water in the boiler flows out of the boiler under the driving action of the pump and reaches the brewing head. At the brewing head, the hot water flows through the water separator into a plurality of uniform small streams of water which flow through the coffee powder cake contained in the powder bowl. The boiler is generally provided with a pressure relief valve, and when the pressure of the pipeline is greater than the rated pressure, the pressure relief valve is opened to maintain the pipeline at a constant pressure. The household coffee machine is generally small in size, and a small water storage boiler or a quick heating boiler is arranged on the household coffee machine by adopting a vibration pump.
The single chip microcomputer program control system is widely used on coffee machines, has an intelligent development trend and is reflected in the appearance and development of intelligent functions such as brewing monitoring, accurate control, quality optimization and the like. Parameters of the coffee machine such as temperature, pressure, coffee liquid volume, boiler liquid level and the like are monitored, and the temperature and the pressure in the high-end coffee machine and the large-scale coffee machine are controlled in a PID closed loop mode.
Coffee quality is very sensitive to brewing parameters such as temperature and pressure, temperature affects coffee flavor by affecting the solubility and molecular kinetic energy of various substances in the coffee, and pressure affects coffee flavor by affecting the scouring force. The household coffee machine is generally provided with a small boiler or a quick-heating boiler, and the temperature of the boiler greatly fluctuates in the brewing process due to small heat capacity. At present, some temperature control modules for controlling the temperature of a boiler mainly adopt a simple PID feedback controller, and the temperature control precision is low in the brewing stage.
The taste indexes of bitterness, sourness, concentration and the like of coffee can generate great difference under different brewing parameters, and the taste preference of users is not uniform, so that the ideal taste index of Italian coffee is not acknowledged. When different types of coffee and different particle sizes are brewed, the taste effect that the user wants to achieve is not necessarily the same. The brewing process of the household Italian coffee machine is fixed, and the various requirements of wide consumers for customizing the brewed Italian coffee cannot be met.
Therefore, by establishing a mathematical model of the boiler of the coffee machine, the design of the feedforward feedback controller can improve the control effect and enable the user to customize brewing on the basis of the control effect.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a customized brewing system and a customized brewing method suitable for a household Italian coffee machine.
The purpose of the invention is realized by the following technical scheme: the invention implements brewing control on the household small boiler Italian coffee machine and the instant boiler Italian coffee machine, thereby realizing customized brewing. The system comprises a coffee machine body, a controller, a sensor, an actuator and a user interaction unit;
the sensor comprises a weighing module, a thermal resistance sensor, a thermocouple sensor and a pressure gauge; the weighing module is used for measuring the weight of coffee liquid flowing out of the coffee machine; the thermal resistance sensor is used for measuring the boiler temperature of the coffee machine; the thermocouple sensor is used for measuring the temperature of the coffee liquid at the outlet of the coffee machine; the pressure gauge is used for measuring the outlet pressure of the vibrating pump of the coffee machine;
the actuator comprises a solid-state relay and a bidirectional rectifying and voltage-reducing module; the solid-state relay is used for switching on and off the heating wire so as to control the heating power of the boiler; the pressure reduction module is used for controlling the power of the vibration pump so as to adjust the brewing pressure;
the controller drives the solid-state relay and the voltage reduction module through feedforward feedback control based on a model, and regulates brewing temperature, pressure and flow curves according to a coffee brewing mode set by a user; the controller obtains controller parameters through a test modeling and simulation method;
the test modeling includes measuring a boiler transfer function and control characteristics of a pump; regarding the boiler as a link of two-in one-out, taking flow and heating power as input, taking the temperature change rate of the boiler as output, and obtaining a discrete transfer function model through a system identification experiment; the control characteristic of the pump refers to the relationship between flow, pressure and controller output (input of the pressure reduction module); since flow control is achieved by reducing the operating voltage of the pump, for convenience, it can be considered that the controller output is directly proportional to the power of the pump; using powder cakes with different thicknesses as constant flow resistance, measuring the relationship between the flow and the pressure under different pump powers within a normal flow range, and obtaining a control characteristic curve of the pump;
in order to reduce the parameter adjusting difficulty of the design of the feedforward feedback controller, an initial parameter is obtained by using a simulation method, and then parameter fine adjustment is carried out by combining with a coffee machine object; designing a static feedforward link of temperature control by using static gain of a boiler transfer function model, and determining a feedforward quantity of pressure control by using a control characteristic curve of a pump; on the basis of the primary real data, the temperature variation caused by the variation output by the controller is solved by using a test model, and simulation output is obtained by superposition; parameter values of the feedback controller can be obtained through simulation design of the controller;
the user interaction unit is used for setting a coffee brewing mode and displaying a measured value curve by a user; the user can select the initial brewing temperature, the temperature gradient mode and the pressure mode, and whether to intervene the large flow, and set the brewing parameters meeting the requirements of the user.
Further, the weighing module is fixed at the coffee outlet, and if a cantilever parallel beam weighing sensor with the measuring range of 1kg can be selected, the cup filled with coffee is weighed, and the weight of the cup filled with coffee is subtracted from the weight of an empty coffee cup to obtain the weight of the coffee; because the density of the coffee is close to that of water and is basically fixed, the volume of the coffee can be obtained through conversion of the coffee weight information; the coffee flow can be obtained by carrying out differential operation on the measured values of the two moments before and after the coffee volume;
the thermal resistance sensor can be used for measuring the temperature of the boiler, has higher precision which can generally reach 0.1 ℃, and is convenient to be applied to temperature control; when the thermal resistor is arranged on the boiler, in order to increase the contact area, the thermal conductive adhesive is adopted and is close to the boiler as much as possible; the casing of the thermal resistor should be as small as possible to reduce temperature measurement lag; in order to connect with the controller, the thermal resistor generally needs to be matched with a transmitting module;
the thermocouple sensor is used for measuring the temperature of the coffee liquid at the outlet of the coffee machine, and the thermal response speed is high; the shell of the thermocouple should be as small as possible to reduce temperature measurement lag, and the shell should meet food hygiene requirements; in order to connect with the controller, the thermocouple generally needs to be matched with a transmitting module;
the pressure gauge is used for measuring the outlet pressure of the vibrating pump of the coffee machine; the digital remote transmission function is required; for a common 9bar coffee machine, the range of the pressure gauge can be selected to be 0-1.6 MPA; the vibration problem of the coffee machine water pump needs to be noticed when the pressure gauge is installed, and a pipeline for connecting the pressure gauge has a pressure bearing function.
The solid-state relay has the advantages that the solid-state relay is convenient to drive by a single chip microcomputer, and an actuator is a linear link; the solid-state relay is generally a thyristor circuit, so that the switching frequency of an input signal cannot be too high, and for the temperature control of a general coffee machine, the selectable control frequency is 2 Hz; for the power regulation of a common household coffee machine vibration pump, a bidirectional rectifying and voltage reducing module is required to be adopted to drive a water pump to normally work.
Further, the obtaining of the boiler transfer function specifically includes:
before carrying out an identification experiment, determining an approximate time constant of a system; inputting a heating power square wave signal with a cycle of 200 seconds and an amplitude of 20% into a system, recording the temperature change condition, and solving the step response transition time T of the system;
in order to simplify the identification experiment, two paths of inputs are respectively identified, and when the relation from one path of input to the output is identified, the other path of input is kept constant; when identifying the transfer function from the heating power to the temperature change rate, a fully extracted cake can be used as a constant flow resistance to keep the flow constant;
identifying the experiment input signal to be a periodic square wave signal, wherein the signal period is more than 2T, the amplitude of the signal is about 20 percent, and the signal time length is about 25 minutes;
considering an ARX model as a system model, identifying the system model by adopting a least square method, and performing low-pass filtering and de-equalization processing on a measured value before carrying out model identification; and selecting a proper model order and a pure hysteresis order to obtain a transfer function of the system.
Further, when the controller detects that the current flow exceeds the upper flow limit, the controller indicates that the brewing powder is placed too little, the powder is ground too coarsely or the powder pressing defect occurs, and the brewing has major errors; in order to make the coffee thicker as much as possible, the controller abandons the pressure set value control and switches to a flow override state, and the flow override adopts a PI controller to reduce the flow below the upper limit of the flow.
Furthermore, temperature rising brewing, constant temperature brewing and cooling brewing can be realized through temperature control, and the temperature control adopts a control method of static feedforward and PID feedback and carries out feedforward aiming at set values of flow and temperature change rate; the brewing in different pressure modes can be realized through pressure control, and the pressure control adopts a static feedforward and PI feedback control method to carry out feedforward aiming at a pressure set value.
Furthermore, the setting range of the initial brewing temperature is 90-110 ℃, the temperature gradient mode comprises cooling brewing, constant-temperature brewing and heating brewing, and a set value curve of the controller is generated according to a mode set by a user to realize customized brewing; when the temperature is reduced and the boiling is carried out, the set value of the temperature change rate controller is-0.15 ℃/s; when the tea is boiled at constant temperature, the set value of the temperature change rate controller is 0 ℃/s; when the temperature is raised and the boiling is carried out, the set value of the temperature change rate controller is 0.15 ℃/s; for a common 9bar home coffee machine, the user selected pressure modes include 9bar, 8bar and 7 bar; when the user selects 9bar for brewing, the pump of the coffee machine works at full power; when the user selects 8bar brewing, the pressure is controlled by a set value with the set value of 8bar when coffee is brewed; when the user selects 7bar brewing, the coffee machine pump works with a lower power; when a user selects to intervene the high flow, and the measured flow value exceeds the upper limit due to the reasons of too coarse powder grinding, too little powder discharging or powder pressing error and the like, the controller enters a flow override control state to reduce the flow below the upper limit of the flow.
Further, the controller communicates with the user interaction unit in a Bluetooth or wireless mode; the user interaction unit comprises, in addition to the selection buttons for setting the initial brewing temperature, the temperature gradient mode and the pressure mode, and whether to intervene in the high flow rate, an editable text box for setting the coffee brewing volume and the upper flow rate limit, and a drawing area for displaying the current boiler temperature, outlet temperature, brewing flow rate, brewing pressure and real-time coffee volume curves, so that the user can know the brewing dynamics.
A customized brewing method suitable for use in a household espresso machine, comprising the steps of:
controlling a water boiling stage: after receiving an instruction of starting to make coffee, the controller controls the temperature in the water boiling stage to enable the temperature of the boiler to reach the set initial brewing temperature and keep stable for a period of time so as to enable the temperature of hot water to be uniform and prevent the temperature control in the brewing stage from being interfered by transient change of the temperature; when the temperature is kept to be stable for a period of time near a set value, entering a brewing stage;
controlling the brewing stage: the method comprises the steps of controlling the temperature change rate of the boiler and the set value of pressure; determining a temperature change rate set value and a pressure set value according to a mode set by a user; driving a solid-state relay and a voltage reduction module to regulate and control the brewing temperature and pressure;
when the volume of the brewed coffee reaches a set value, making a cup of coffee is finished, and brewing is stopped.
Further, before the control of the brewing stage, judging whether pre-soaking is needed according to the setting of a user, wherein the pre-soaking mode is to open an outlet valve, close a pump, allow residual hot water in a pipeline to flow into the pressed powder under the condition of no pressurization, wet the pressed powder, expand the pressed powder and enable the pressed powder to be more impact-resistant; after the presoaking is finished, the pump is started, and the control of the brewing stage is started.
Furthermore, when a user sets the intervention on the large flow, when the controller detects that the current flow exceeds the upper limit of the flow, the situation that the powder is placed too little, the powder is ground too coarsely or the powder pressing defect occurs indicates that the great error occurs in the brewing process; in order to make the coffee thicker as much as possible, the controller should give up the pressure set value control and switch to the flow override state to reduce the flow below the upper flow limit.
The invention has the beneficial effects that: a controller, a sensor, an actuator and a user interaction unit are set up on the basis of a common coffee machine to form a customized brewing system; the controller drives the solid-state relay and the voltage reduction module through feedforward feedback control based on a model, and regulates brewing temperature, pressure and flow curves according to a coffee brewing mode set by a user; the controller obtains controller parameters through a test modeling and simulation method; by establishing a mathematical model of the coffee machine boiler, the control effect can be improved by designing a feedforward feedback controller; the user can select the initial brewing temperature, the temperature gradient mode and the pressure mode, and whether to intervene the large flow, and set the brewing parameters meeting the needs of the user; on the basis of program control of a common coffee machine, the invention improves the brewing quality of the concentrated coffee by controlling brewing process parameters, so that a user can adjust the taste by himself to meet the brewing requirement.
Drawings
FIG. 1 illustrates the steps of performing customized brewing;
FIG. 2 is a control strategy for a controller;
fig. 3 is a customized brewing case.
Detailed Description
In order to facilitate understanding of those skilled in the art, the following description will be further made with reference to the accompanying drawings and examples.
The specific implementation of the invention can be divided into four parts of measurement and control system construction, system test modeling, simulation parameter adjustment and user interaction unit design, as shown in fig. 1.
The first part is constructed for a measurement and control system. The measurement and control system consists of a sensor and an actuator; the sensor comprises a weighing module, a thermal resistance sensor, a thermocouple sensor and a pressure gauge; the weighing module is used for measuring the weight of coffee liquid flowing out of the coffee machine; the thermal resistance sensor is used for measuring the boiler temperature of the coffee machine; the thermocouple sensor is used for measuring the temperature of the coffee liquid at the outlet of the coffee machine; the pressure gauge is used for measuring the outlet pressure of the vibrating pump of the coffee machine; the actuator comprises a solid-state relay and a bidirectional rectifying and voltage-reducing module; the solid-state relay is used for switching on and off the heating wire so as to control the heating power of the boiler; the pressure reduction module is used for controlling the power of the vibration pump so as to adjust the brewing pressure;
the weighing module is fixed at the coffee outlet, and if a cantilever parallel beam weighing sensor with the measuring range of 1kg can be selected, the cup filled with coffee is weighed, and the weight of the cup filled with coffee is subtracted from the weight of an empty coffee cup to obtain the weight of the coffee; because the density of the coffee is close to that of water and is basically fixed, the volume of the coffee can be obtained through conversion of the coffee weight information; the coffee flow can be obtained by carrying out differential operation on the measured values of the two moments before and after the coffee volume;
the thermal resistance sensor can be used for measuring the temperature of the boiler, has higher precision which can generally reach 0.1 ℃, and is convenient to be applied to temperature control; when the thermal resistor is arranged on the boiler, in order to increase the contact area, the thermal conductive adhesive is adopted and is close to the boiler as much as possible; the casing of the thermal resistor should be as small as possible to reduce temperature measurement lag; in order to connect with the controller, the thermal resistor generally needs to be matched with a transmitting module;
the thermocouple sensor is used for measuring the temperature of the coffee liquid at the outlet of the coffee machine, and the thermal response speed is high; the shell of the thermocouple should be as small as possible to reduce temperature measurement lag, and the shell should meet food hygiene requirements; in order to connect with the controller, the thermocouple generally needs to be matched with a transmitting module;
the pressure gauge is used for measuring the outlet pressure of the vibrating pump of the coffee machine; the digital remote transmission function is required; for a common 9bar coffee machine, the range of the pressure gauge can be selected to be 0-1.6 MPA; the vibration problem of the coffee machine water pump needs to be noticed when the pressure gauge is installed, and a pipeline for connecting the pressure gauge has a pressure bearing function.
The solid-state relay has the advantages that the solid-state relay is convenient to drive by a single chip microcomputer, and an actuator is a linear link; the solid-state relay is generally a thyristor circuit, so that the switching frequency of an input signal cannot be too high, and for the temperature control of a general coffee machine, the selectable control frequency is 2 Hz; for the power regulation of a common household coffee machine vibration pump, a bidirectional rectifying and voltage reducing module is required to be adopted to drive a water pump to normally work.
The second part is system test modeling, and measures the boiler transfer function and the control characteristics of the pump.
Regarding the boiler as a link of two-in one-out, taking flow and heating power as input, taking the temperature change rate of the boiler as output, and obtaining a discrete transfer function model through a system identification experiment; before carrying out an identification experiment, determining an approximate time constant of a system; inputting a heating power square wave signal with a cycle of 200 seconds and an amplitude of 20% into a system, recording the temperature change condition, and solving the step response transition time T of the system; in order to simplify the identification experiment, two paths of inputs are respectively identified, and when the relation from one path of input to the output is identified, the other path of input is kept constant; when identifying the transfer function from the heating power to the temperature change rate, a fully extracted cake can be used as a constant flow resistance to keep the flow constant; identifying the experiment input signal to be a periodic square wave signal, wherein the signal period is more than 2T, the amplitude of the signal is about 20 percent, and the signal time length is about 25 minutes; considering an ARX model as a system model, identifying the system model by adopting a least square method, and performing low-pass filtering and de-equalization processing on a measured value before carrying out model identification; and selecting a proper model order and a pure hysteresis order to obtain a transfer function of the system.
The control characteristic of the pump refers to the relationship between flow, pressure and controller output (input of the pressure reduction module); since flow control is achieved by reducing the operating voltage of the pump, for convenience, it can be considered that the controller output is directly proportional to the power of the pump; and (3) using the powder cakes with different thicknesses as constant flow resistance, and measuring the relation between the flow and the pressure under different pump powers within a normal flow range to obtain a control characteristic curve of the pump.
The third part is simulation parameter adjustment. In order to reduce the parameter adjusting difficulty of the design of the feedforward feedback controller, initial parameters are obtained by a simulation method, and then parameter fine adjustment is carried out by combining with a coffee machine object.
As shown in fig. 2, during the process of making a cup of coffee, the controller acts in the following stages: after receiving an instruction of starting to make coffee, the control of the water boiling stage is firstly carried out, so that the temperature of the boiler reaches the set initial brewing temperature, and the boiler is kept stable for a period of time, so that the temperature of hot water reaches uniformity, and the temperature control of the brewing stage is prevented from being interfered by transient change of the temperature. And entering a brewing stage after the temperature is kept around the set value for a period of time and is stabilized. First, whether pre-soaking is required is judged according to user setting. The pre-soak is done by opening the outlet valve, closing the pump, allowing the residual hot water in the pipe to flow into the cake without pressurization, wetting the cake, causing it to expand and become more impact resistant. After the presoaking is finished, the pump is started, and the control of the brewing stage is started, which mainly comprises the control of the set values of the temperature change rate and the pressure of the boiler. And determining a temperature change rate set value and a pressure set value according to a mode set by a user. If the user sets a compensation function for large flow, when the controller detects that the current flow exceeds the upper limit of the flow, the situation that the powder is placed too little, the grinding is too coarse or the powder pressing defect occurs indicates that great errors occur in the brewing process. To make the coffee stronger as possible, the controller should forego the pressure set point control and switch to the flow override control state. When the volume of the brewed coffee reaches a set value, making a cup of coffee is finished, and brewing is stopped. In order to realize automatic brewing, the controller should take over the switching of the pump, the outlet valve, etc.
The temperature, pressure and flow measurement values are low-pass filtered, then applied to a control algorithm, and the controller output is calculated. The set point of the temperature control during the water boiling phase is specified by the initial brewing temperature specified by the user, and the function is to cause the boiler hot water to reach the preset temperature and then start to brew coffee. The heating brewing, the constant-temperature brewing and the cooling brewing can be realized by the set value control of the temperature change rate, and the set value control of the temperature change rate adopts a control method of static feedforward and PID feedback and carries out feedforward aiming at the set values of the flow and the temperature change rate. The boiling in different pressure modes can be realized by the control of the set value of the pressure, and the control of the set value of the pressure adopts a control method of static feedforward and PI feedback to carry out feedforward aiming at the set value of the pressure. The flow override control uses a PI controller. The controller output is the sum of the feedforward quantity and the feedback quantity. The feedback part only works under the condition that the controlled parameter is stable, and the phenomenon that the controller is interfered by the violent change of the controlled parameter at the initial stage of the brewing stage of the coffee machine is prevented. The feedback part of the controller adopts position PID, and integral cutting is carried out when a large error or integral action is too strong.
And designing a static feedforward link of temperature control by testing the static gain of the boiler transfer function model obtained by modeling, and obtaining a parameter value of the PID feedback controller by simulation design of the controller. During simulation parameter adjustment, on the basis of one-time real temperature data, in each control period, a real temperature measured value is read firstly, then temperature variation caused by variation output by the controller is solved according to a heating channel transfer function model obtained through identification, the temperature variation and the temperature variation are added to obtain a temperature measured value during simulation, the temperature measured value is used for calculating the output of the controller, and the operation is repeated.
The feed forward amount of the pressure control is determined using the control characteristic of the pump. According to the control characteristic curve of the pump measured by the coffee machine test modeling, when the flow is fixed to the ideal flow, the output of the flow controller is approximately in a linear relation with the pressure, and the feedforward quantity of the pressure control can be designed according to the relation. The PI feedback controller for pressure control is simple in design, and can achieve a control target by adopting weaker proportional and integral action. When debugging the PI controller, the impact of the controller output oscillation on the pressed powder is prevented.
The fourth part is designed for a user interaction unit, and the user interaction unit is used for setting a coffee brewing mode and displaying a measured value curve by a user so as to set the brewing customization requirement and monitor the actual control effect.
The user can select an initial brewing temperature, a temperature gradient mode and a pressure mode, and whether to intervene in large flow, the setting range of the initial brewing temperature is 90-110 ℃, and the temperature gradient mode comprises cooling brewing, constant-temperature brewing and heating brewing. And generating a set value curve of the controller according to a mode set by a user to realize customized brewing. When the temperature is reduced and the boiling is carried out, the set value of the temperature change rate controller is-0.15 ℃/s; when the tea is boiled at constant temperature, the set value of the temperature change rate controller is 0 ℃/s; when the temperature is increased and the boiling is carried out, the set value of the temperature change rate controller is 0.15 ℃/s. For a common 9bar home coffee maker, the pressure modes selected by the user include 9bar, 8bar and 7 bar. When the user selects 9bar for brewing, the pump of the coffee machine works at full power; when the user selects 8bar brewing, the pressure is controlled by a set value with the set value of 8bar when coffee is brewed; when the user selects 7bar brewing, the coffee machine pump operates at a lower power. When a user selects to intervene the high flow, and the measured flow value exceeds the upper limit due to the reasons of too coarse powder grinding, too little powder discharging or powder pressing error and the like, the controller enters a flow override control state to reduce the flow below the upper limit of the flow.
The user interaction unit can be made in the form of a mobile phone APP and the like, and the controller is communicated with the user interaction unit in a Bluetooth or wireless mode. The user interaction unit comprises, in addition to selection buttons for setting the initial brewing temperature, the temperature gradient mode and the pressure mode, and whether to intervene in the high flow rate, editable text boxes for setting the coffee brewing volume, the upper flow rate limit, etc., and drawing areas for displaying the current boiler temperature, outlet temperature, brewing flow rate, brewing pressure, real-time coffee volume curves, so that the user can understand the brewing dynamics.
Fig. 3 is a one-time customized brewing case, and the temperature of the boiler can be controlled to be constant, rising and falling by setting a temperature mode, and the quality indexes such as sourness, taste and concentration are influenced.
The technical principle of the present invention is described above in connection with specific embodiments. The description is made for the purpose of illustrating the principles of the invention and should not be construed in any way as limiting the scope of the invention. Based on the explanations herein, those skilled in the art will be able to conceive of other embodiments of the present invention without inventive effort, which would fall within the scope of the present invention.
Claims (10)
1. A customized brewing system suitable for a household Italian coffee machine is characterized by comprising a coffee machine body, a controller, a sensor, an actuator and a user interaction unit;
the sensor comprises a weighing module, a thermal resistance sensor, a thermocouple sensor and a pressure gauge; the weighing module is used for measuring the weight of coffee liquid flowing out of the coffee machine; the thermal resistance sensor is used for measuring the boiler temperature of the coffee machine; the thermocouple sensor is used for measuring the temperature of the coffee liquid at the outlet of the coffee machine; the pressure gauge is used for measuring the outlet pressure of the vibrating pump of the coffee machine;
the actuator comprises a solid-state relay and a voltage reduction module; the solid-state relay is used for switching on and off the heating wire so as to control the heating power of the boiler; the pressure reduction module is used for controlling the power of the vibration pump so as to adjust the brewing pressure;
the controller drives the solid-state relay and the voltage reduction module through feedforward feedback control based on a model, and regulates brewing temperature, pressure and flow curves according to a coffee brewing mode set by a user; the controller obtains controller parameters through a test modeling and simulation method;
the test modeling includes measuring a boiler transfer function and control characteristics of a pump; regarding the boiler as a link of two-in one-out, taking flow and heating power as input, taking the temperature change rate of the boiler as output, and obtaining a boiler transfer function model through a system identification experiment; using powder cakes with different thicknesses as constant flow resistance, measuring the relationship between the flow and the pressure under different pump powers within a normal flow range, and obtaining a control characteristic curve of the pump;
obtaining initial parameters designed by a feedforward feedback controller by using a simulation method, and then finely adjusting the parameters by combining with a coffee machine object; designing a static feedforward link of temperature control by using static gain of a boiler transfer function model, and determining a feedforward quantity of pressure control by using a control characteristic curve of a pump; on the basis of the primary real data, the temperature variation caused by the variation output by the controller is solved by using a test model, and simulation output is obtained by superposition;
the user interaction unit is used for setting a coffee brewing mode and displaying a measured value curve by a user; the user can select the initial brewing temperature, the temperature gradient mode and the pressure mode, and whether to intervene the large flow, and set the brewing parameters meeting the requirements of the user.
2. The customized brewing system for a home espresso machine according to claim 1, wherein the weighing module is fixed at the coffee outlet for weighing a cup containing coffee and subtracting the weight of an empty coffee cup to obtain the weight of coffee; converting the weight information of the coffee to obtain the volume of the coffee; carrying out differential operation on the measured values of the two moments before and after the coffee volume to obtain the coffee flow; the thermal resistance sensor is used for measuring the temperature of the boiler, and when the thermal resistance sensor is installed on the boiler, heat-conducting glue is adopted and is close to the boiler as much as possible; the casing of the thermal resistor should be as small as possible to reduce temperature measurement lag; the thermocouple sensor is used for measuring the temperature of coffee liquid at the outlet of the coffee machine, the shell of the thermocouple should be as small as possible to reduce the temperature measurement lag, and the shell should meet the food hygiene requirement; the pressure gauge is used for measuring the pressure of the outlet of the vibrating pump of the coffee machine and has a digital remote transmission function, and a pipeline connected with the pressure gauge has a pressure bearing function.
3. The customized brewing system for a household espresso machine according to claim 1, wherein the obtaining of the boiler transfer function comprises in particular:
before carrying out an identification experiment, determining an approximate time constant of a system; inputting a heating power square wave signal with a cycle of 200 seconds and an amplitude of 20% into a system, recording the temperature change condition, and solving the step response transition time T of the system;
respectively identifying the two paths of input, wherein when the relation from one path of input to the output is identified, the other path of input is kept constant; when a transfer function from heating power to temperature change rate is identified, a fully extracted powder cake is used as a constant flow resistance to keep the flow constant;
identifying that the experimental input signal adopts a periodic square wave signal, wherein the signal period is more than 2T, the signal amplitude is 20 percent, and the signal time length is 25 minutes;
considering an ARX model as a system model, identifying the system model by adopting a least square method, and performing low-pass filtering and de-equalization processing on a measured value before carrying out model identification; determining the model order and the pure lag order yields the transfer function of the system.
4. The customized brewing system for use with a home espresso machine according to claim 1, wherein the controller detects that the current flow rate exceeds an upper flow rate limit indicating a significant brewing fault, the controller overrides the pressure set point control and switches to a flow override state, and the flow override state reduces the flow rate below the upper flow rate limit using a PI controller.
5. The customized brewing system suitable for the household Italian coffee machine according to claim 1, wherein the temperature control is realized by temperature control, wherein the temperature control adopts a static feedforward and PID feedback control method and carries out feedforward aiming at set values of flow and temperature change rate; the brewing in different pressure modes can be realized through pressure control, and the pressure control adopts a static feedforward and PI feedback control method to carry out feedforward aiming at a pressure set value.
6. The customized brewing system for the Italian coffee machine for household use according to claim 1, wherein the initial brewing temperature is set in a range of 90-110 ℃, the temperature gradient mode comprises cooling brewing, constant-temperature brewing and heating brewing, and a set value curve of the controller is generated according to a mode set by a user to realize customized brewing; when the temperature is reduced and the boiling is carried out, the set value of the temperature change rate controller is-0.15 ℃/s; when the tea is boiled at constant temperature, the set value of the temperature change rate controller is 0 ℃/s; when the temperature is raised and the boiling is carried out, the set value of the temperature change rate controller is 0.15 ℃/s; for a common 9bar home coffee machine, the user selected pressure modes include 9bar, 8bar and 7 bar; when the user selects 9bar for brewing, the pump of the coffee machine works at full power; when the user selects 8bar brewing, the pressure is controlled by a set value with the set value of 8bar when coffee is brewed; when the user selects 7bar brewing, the coffee machine pump operates at a lower power.
7. The customized brewing system for a household espresso machine according to claim 1, wherein the controller communicates with the user interaction unit via bluetooth or wirelessly; the user interaction unit comprises, in addition to the selection buttons for setting the initial brewing temperature, the temperature gradient mode and the pressure mode, and whether to intervene in the high flow rate, an editable text box for setting the coffee brewing volume and the upper flow rate limit, and a drawing area for displaying the current boiler temperature, outlet temperature, brewing flow rate, brewing pressure and real-time coffee volume curves, so that the user can know the brewing dynamics.
8. Method for customized brewing of coffee by means of a system according to any of claims 1-7, characterized in that it comprises the following steps:
controlling a water boiling stage: after receiving an instruction of starting to make coffee, the controller controls the temperature in the water boiling stage to ensure that the temperature of the boiler reaches the set initial brewing temperature, keeps stable for a period of time and then enters the brewing stage;
controlling the brewing stage: the method comprises the steps of controlling the temperature change rate of the boiler and the set value of pressure; determining a temperature change rate set value and a pressure set value according to a mode set by a user; driving a solid-state relay and a voltage reduction module to regulate and control the brewing temperature and pressure;
when the volume of the brewed coffee reaches a set value, making a cup of coffee is finished, and brewing is stopped.
9. The method of claim 8, wherein prior to the brewing phase control, it is determined from the user setting whether pre-soaking is required by opening an outlet valve, closing a pump, allowing residual hot water in the pipe to flow into the cake without pressurization, wetting the cake, causing it to expand and become more impact resistant; after the presoaking is finished, the pump is started, and the control of the brewing stage is started.
10. The method of claim 8, wherein when the user sets an intervention for a high flow rate, and the controller detects that the current flow rate exceeds the upper flow rate limit, indicating a significant brewing error, the controller overrides the pressure set point control and switches to a flow override state to reduce the flow rate below the upper flow rate limit.
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| CN113425161B (en) * | 2021-07-27 | 2023-09-05 | 北京镁伽机器人科技有限公司 | Beverage making parameter configuration method and system and beverage making method and device |
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