Food preparation device with overpressure detection

Abstract

The invention concerns a food preparation device 1 comprising a food preparation pot 2, a heating element 3 for heating food 4 in the food preparation pot 2, a tool 5 for blending and/or comminuting food 4 in the food preparation pot 2, a lid 6, 7 for the food preparation pot 2, and an electric motor 8 for rotating the tool 5. A monitoring unit monitors a power input of the electric motor 8 for detecting an overpressure in the food preparation pot 2. The invention also concerns a method and a computer program product. A very reliable detection of overpressure can thereby be enabled.

Claims

1. A food preparation device comprising a food preparation pot, a heating element for heating food in the food preparation pot, a tool for blending and/or comminuting food in the food preparation pot, a lid for the food preparation pot, and an electric motor for rotating the tool, wherein the food preparation device further comprises a monitoring unit configured to monitor a power input of the electric motor and to detect an overpressure in the food preparation pot based at least in part on the monitored power input, wherein the overpressure comprises vapor pressure inside the food preparation pot being greater than ambient pressure.

2. The food preparation device of claim 1, wherein the monitoring unit is configured to modify a food preparation parameter and/or a recipe for food based on the monitored power input of the electric motor.

3. The food preparation device of claim 1, wherein the food preparation device is configured such that, during operation, a notification for the user is provided based on the monitored power input of the electric motor.

4. The food preparation device of claim 1, wherein the food preparation device is configured such that, during operation, a locking unit for the lid is engaged or disengaged based on the monitored power input of the electric motor.

5. The food preparation device of claim 1, wherein the food preparation device is configured such that, during operation, an overpressure is detected by comparing the monitored power input of the electric motor before and after a boiling point (t.sub.S) of a liquid or a selected temperature in the food preparation pot has been exceeded.

6. The food preparation device of claim 1, wherein the food preparation device is configured such that, during operation, the monitoring unit monitors the power input of the electric motor for the detection of an overpressure in the food preparation pot only when a minimum temperature in the food preparation pot is reached.

7. The food preparation device of claim 1, wherein the monitoring unit is configured such that a monitoring event is output by the monitoring unit when a monitoring value, which is determined based on the monitored power input of the electric motor, reaches a detection threshold (M).

8. The food preparation device of claim 7, wherein the monitoring value corresponds to a moving average value (K.sub.g), a variation amplitude (K.sub.A) and/or a fundamental frequency (K.sub.F) of the captured power input of the electric motor.

9. The food preparation device of claim 7, wherein the detection threshold (M) is a travelling threshold or an absolute threshold.

10. The food preparation device of claim 7, wherein the food preparation device is configured such that, during operation, the detection threshold (M) is determined based on the monitored power input of the electric motor after a minimum temperature has been reached and/or before a maximum temperature or a boiling point (t.sub.S) has been reached.

11. The food preparation device of claim 7, wherein that the food preparation device is configured such that, during operation, only after a selected temperature or the boiling point (t.sub.S) has been reached, it is determined for monitoring the monitoring event whether the monitoring value reaches the detection threshold (M).

12. The food preparation device of claim 1, wherein the power input is determined through the motor current (I) for the electric motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) It is shown:

(2) FIG. 1: Schematical front view of a food preparation device with a food preparation pot shown in cross-section;

(3) FIG. 2: Schematical illustration of a course of the power input of the electric motor over time during the preparation of a water-containing food in a food preparation pot;

(4) FIG. 3: Schematical representation of a block diagram for signal processing of the power input in the form of the motor current with illustrations I to IV of the thereby successively occurring signal changes over the time axis.

DETAILED DESCRIPTION

(5) FIG. 1 shows a food preparation unit 1 with a food preparation pot 2, in which a water-containing food such as soup is being cooked. The food 4 is heated by a heating element 3 and the temperature of the food 4 or in the food preparation pot 2 is measured approximately by the temperature sensor 13. A tool 5, in particular a mixing knife with radially projecting blades, for blending and/or comminuting food 4 in the food preparation pot 2 rotates during heating in order to avoid burning (of the food). An electric motor 8 can drive the tool 5 via a drive shaft 16, which extends through a pot feedthrough 17 to the tool 5 inside the food preparation pot 2. A data processing unit 10 with a processor 11 and a memory 12 is particularly integrated in the housing 15. A user interface 18 with a display and/or a control switch is also integrated in the housing 15.

(6) A lid 6, 7 covers the open top side of the food preparation pot 2 and comprises a first lid element 6 and a second lid element 7. The disc-shaped first lid element 6 rests on the food preparation pot 2 and has a central lid opening 14 for inserting ingredients into the food preparation pot 2. The separate second lid element 7 serves to cover the lid opening 14. When cooking the food 4, rising steam 20 forms and the pressure in the food preparation pot 2 increases, especially after reaching the boiling point. In the case of overpressure, a compressive force occurs which acts in the direction of the pot bottom 22, so that an increased load or axial load on the drive shaft 16 causes increased friction in the bearing of the drive shaft 16. The increased friction in turn increases the load on the electric motor 8, which leads to a higher power input.

(7) In particular, an increased current input can therefore be observed when overpressure is generated. The motor current I supplied to the electric motor 8 then increases as shown in FIG. 2.

(8) FIG. 2 shows the motor current I over time tin a time window where the temperature just exceeds the boiling point at the time t.sub.S. The steam 21 escapes for example intermittently as illustrated in FIG. 1. In particular, a series of smaller quantities of leaking steam 21 may escape as a result of overpressure. Having such leaking or leakings, the pressure drops abruptly by small amounts and rises again immediately. The load on the electric motor 8 can therefore fluctuate correspondingly more strongly compared to the cooking process without overpressure, especially before reaching the boiling point or a selected temperature. The greater variation of the load can lead to an increased fundamental frequency F and/or an increased amplitude A of the motor current I, as schematically illustrated in FIG. 2 by the curves K.sub.F (frequency curve) and K.sub.A (amplitude curve). Basically, when an overpressure occurs, the equilibrium of the complex system of motor control, friction losses, temperature and pressure increase, and motor behavior can change when the boiling point is exceeded. This can then be reflected in the changed power input over time. For reliable detection, it is therefore preferable to monitor the motor power input and its change when the boiling point is reached.

(9) A pressure increase can therefore be inferred if the above described phenomena are observed or detected by the automatically operating monitoring unit with the aid of correspondingly defined detection criteria, which take into account, for example, the increased power input, an increased noise, the increased frequency of the fundamental oscillation, the increased oscillation amplitude of the fundamental oscillation or a characteristic curve of the power input over time. If a detection criterion for a specified monitoring event related to a certain degree of overpressure is met, the user is for example given a corresponding message in the form of a notification on the display.

(10) The detection accuracy can be further improved by comparing the data before reaching the boiling point with the data after exceeding the boiling point. This is explained below by an example where the monitoring unit is arranged to monitor the monitoring event “Overpressure is present”, which informs the user that the cooking result may be affected by an overpressure and prompting the user to reduce the cooking time. Alternatively, the cooking time can be reduced automatically. In this example, a soup is cooked. The temperature in the food preparation pot 2 rises, as schematically illustrated in FIG. 2. When a defined minimum temperature of 90° C. is reached (in FIG. 2 at the time t.sub.90° C.), a moving average M1 for the later detection threshold M is calculated continuously by a corresponding algorithm on the basis of the recorded motor current I or curve k1. When a defined maximum temperature of 96° C. is reached, the moving average M1 calculated at that time t.sub.96° C. forms the detection threshold M for the monitoring event “Overpressure is present”. Alternatively or additionally, the moving average M1 can be determined permanently until the boiling point is reached.

(11) When a selected temperature or boiling point is reached, the moving average M1 of this time t.sub.S used as the detection threshold M, which is preferably constant, for monitoring the monitoring event. As FIG. 2 shows, the algorithm for the moving average M1 and thus for the detection threshold M includes a factor, e.g. 1.25, so that the detection threshold M is e.g. 25% higher compared to the moving average value Kg during the reference recording of the power input before reaching the selected temperature or boiling point t.sub.S. In one embodiment, the reference measurement is carried out in particular within a time period that is dependent on the temperature, e.g. between the points in time t.sub.90° C. to t.sub.96° C., i.e. from a temperature of 90° C. to a temperature of 96° C.

(12) In the example of FIG. 2, from the time t.sub.S on, the moving average value Kg using the detection threshold M is monitored once the boiling point is exceeded, i.e. 100° C. for food 4. The moving average value Kg is calculated on the basis of the motor current I that is recorded. In FIG. 2, curve k1 refers to the moving average value Kg before the boiling point and curve k2 to after the boiling point. When the moving average value Kg or curve k2 reaches the detection threshold M, the monitoring event “Overpressure is present” is detected. In FIG. 2, however, the moving average value Kg has yet not reached the detection threshold M. The overpressure is therefore, based on the monitoring, currently irrelevant for the prepared soup. Previously described measures would only be initiated upon detection of the monitoring event.

(13) The reliability of the monitoring can be further increased by improving the processing and/or filtering of the signal of the power input or of the motor current I. For example, a monitoring value W can thereby be obtained. FIG. 3 shows an example of such signal processing using a block diagram. MC is the motor current I (see diagram I of FIG. 3).

(14) The block diagram symbol with the input signal “yin” and the output signal “ed” represents a filter, in particular a so-called unknown-input-observer, which is preferably arranged such that the fundamental oscillation and/or the direct component of the input signal “yin” are removed (see diagram II of FIG. 3). “Yin” corresponds to the motor current I, i.e. the motor current signal. Preferably, the filter comprises a multi-dimensional integrator, preferably of the type “1/s”. In one embodiment, the output signal “ed” is squared, which is indicated by the block diagram symbol “|u.sup.2|” in FIG. 3. Diagram III of FIG. 3 shows the resulting output signal.

(15) In one embodiment, a further signal processing step or a further signal processing module is provided between this resulting output signal and the monitoring value W, which are arranged as described below.

(16) A first-order delay element is provided which can typically be described by the following differential equation with a time constant T, a factor K, an input signal v(t) dependent on time t and an output signal y(t) also dependent on time t as well as its derivative {dot over (y)}(t):
T.Math.{dot over (y)}(t)+y(t)=K.Math.v(t)

(17) The noise can be smoothed by means of the first-order delay element. The triangular block diagram symbol “-K-” indicates an amplification factor. The amplification factor of the block diagram symbol “-K-” and the factor K of the differential equation can be different factors. The block symbol “Int1” refers to an integrator of the type indicated in the block diagram symbol.

(18) In general, a food preparation device can be an oven, an automated cooker, a food processor or a pressure cooker. During operation, a food and/or ingredient is placed in the food preparation pot 2 and the food 4 is prepared in food preparation pot 2. In particular, the tool 5 and/or the heating element 3 are located near the bottom of the food preparation pot 2.