COOKING APPLIANCE AND METHOD FOR OPERATING A COOKING APPLIANCE

Abstract

In a method for operating a cooking appliance, a measurement profile is recorded of a light reflected by a food during a heat treatment cycle. A time instant of a turning point is determined from the measurement profile, and an action is triggered on the basis of the determined time instant of this turning point.

Claims

1-15 (canceled)

16. A method for operating a cooking appliance, said method comprising: recording a measurement profile of a light reflected by a food during a heat treatment cycle; determining a time instant of a turning point from the measurement profile; and triggering an action on the basis of the determined time instant of this turning point.

17. The method of claim 16, wherein the measurement profile is recorded in a wavelength range.

18. The method of claim 16, wherein a number of measurement profiles are recorded in different wavelength ranges.

19. The method of claim 16, wherein the measurement profile is a profile of a brightness, a color saturation or a color tone of the reflected light.

20. The method of claim 16, wherein the time instant of the turning point of the measurement profile is determined between an accelerating decrease and a subsequently slowing decrease in the measurement profile.

21. The method of claim 20, wherein the measurement profile is a brightness.

22. The method of claim 16, wherein the time instant of the turning point of the measurement profile is determined between an accelerating increase and a subsequently slowing increase in the measurement profile.

23. The method of claim 22, wherein the measurement profile is a color saturation or a color tone.

24. The method of claim 16, wherein the time instant of the turning point is calculated from a determination of an extreme value of a differential profile of a first order.

25. The method of claim 24, wherein the extreme value of the differential profile is a minimum.

26. The method of claim 16, wherein the time instant of the turning point is calculated from a determination of a turning point of a differential profile of a second order.

27. The method of claim 16, wherein the action is triggered when the time instant of the turning point is reached.

28. The method of claim 16, wherein the action is triggered, when the time instant of the turning point, plus a predefined and/or user-defined time offset, is reached.

29. The method of claim 16, wherein the measurement profile is smoothed.

30. The method of claim 16, wherein the measurement profile is recorded after an initial start duration of the heat treatment cycle has elapsed.

31. The method of claim 16, further comprising increasing a measurement rate when approaching the turning point.

32. The method of claim 16, wherein the time instant is determined by predicting the measurement profile.

33. A cooking appliance configured for carrying out a method as set forth in claim 16, said cooking appliance comprising: a light source directing light at food in a cooking compartment; a light sensor directed at the food to receive light reflected by the food; an evaluation device configured to store a measurement profile recorded of the light reflected by the food during a heat treatment cycle and to determine a time instant of a turning point from the measurement profile; and a control device configured to trigger an action on the basis of the determined time instant of the turning point.

Description

[0058] The above-described properties, features and advantages of this invention and the manner in which these are achieved will become clearer and more readily understandable in connection with the following schematic description of an exemplary embodiment, which will be described in further detail making reference to the drawings.

[0059] FIG. 1 shows a sectional representation in a side view of a household cooking appliance in the form of an oven; and

[0060] FIG. 2 shows steps of a possible method for determining the reaching of a target level of browning based on the time instant tw of the turning point of a brightness profile; and

[0061] FIG. 3 shows a brightness run produced during the method and the first and second difference quotients thereof, which can be evaluated individually or in combination for determining the time instant tw.

[0062] FIG. 1 shows a household cooking appliance in the form of an oven 1. The oven 1 has a cooking compartment 2, which can be heated by means of at least one heating apparatus 3. Food product G, which is accommodated here in an item of cookware in the form of a dish S, can be introduced in the cooking compartment 2. The dish S is placed on a baking tray B.

[0063] The oven 1 also has a number of light sources introduced behind a cooking compartment wall or muffle 5 in the form of a number of LEDs 6 producing white light, the light of which falls into the cooking compartment 2 through at least one opening in the muffle 5. The at least one opening can be covered by a viewing window (not shown).

[0064] The oven 1 also has a light sensor introduced, in a ceiling of the oven muffle 5, in the form of a camera 7. The camera 7 is sensitive here for instance to the visible or “white” spectral range. A field of view F of the camera 7 is aligned here purely vertically, by way of example, and comprises parts of the muffle 5 and also the baking tray B with the dish S placed thereon. The camera 7 can be arranged in particular so that it does not directly receive light emitted by an LED 6 and also no mirroring reflex on the muffle 5. The camera 7 receives and measures therefore practically only diffusely reflected scatter light. Should however specularly reflected light be incident into the camera 7, such a reflection reflex can be detected and suppressed e.g. faded out.

[0065] The oven 1 moreover has a control device 8 provided with a data memory, said control device being used to control the oven 1, for instance to control cooking programs. It can activate the heating apparatus 3, for instance. The control device 8 can also actuate the LEDs 6 and the camera 7 and is also used to evaluate the measurement results (images) determined by the camera 7. The images are constructed on a pixel basis and have a resolution for example of 512×512 or 2048×1024 pixels.

[0066] The control device 8 is also used as an evaluation device for storing at least one measurement profile of a brightness of the food product G and for determining the time instant tw of the turning point of the measurement profile. The control device 8 can also be used for target analysis of the food product G, so that the food product G is identified and is isolated in terms of image from its surroundings. In order to record the measurement profile, only the pixels assigned to the food product G can then be used. It is in particular possible to identify different food products G and evaluate the same separately by means of target analysis.

[0067] FIG. 2 shows steps of a possible method for determining the reaching of a target level of browning based on the time instant tw of the turning point of a profile of a black-white brightness. FIG. 3 shows a number of brightness profiles which can be produced during the method and which can be evaluated in order to determine the time instant tw, namely a measurement profile V0, a differential profile of the first order V1 and a differential profile of the second order V2. In particular, the differential profile of the first order V1 corresponds to the first differential quotients of the measurement profile VO and the differential profile of the second order V2 corresponds to the second differential quotients of the measurement profile V0 or the first differential quotients of the differential profile of the first order V1.

[0068] With respect to FIG. 2, in a first step S2 of a heat treatment cycle, the heating apparatus 3 can be switched on by the control device 8, namely in the food product located in the cooking compartment 2.

[0069] In an optional step S2, an initial duration ta (e.g. between 3 and 8 minutes) can then be expected, before images which show the food product G are recorded from the cooking compartment 2 by means of the camera 7.

[0070] In step S3, at the end of the initial period of time ta, an image is recorded from the cooking compartment 2 by means of the camera 7, and triggered by the control device 8. To this end, the control device 8 can simultaneously activate the LEDs 6 in order to provide an adequately high object brightness.

[0071] In step S4, the control device 8 carries out a target analysis of the food product G on the basis of the first image, possibly also on the basis of each image, and isolates its pixels in the image with respect to its environment.

[0072] In step S4, further methods of image processing can also be applied, e.g. a pretreatment of the pixels for instance a white balance for highlighting changes in brightness.

[0073] In step S5, the control device 8 only averages the pixels of the food product G in respect of its brightness, in particular arithmetically, so that a single brightness measured value h.sub.avg is determined for the food product G. An arbitrary scale of this brightness measured value h.sub.avg is shown in FIG. 3 on the left x-axis.

[0074] In a step S6, at least after reaching a specific number of measured values, the last determined measured value is smoothed by means of the control device 8, e.g. by the method of the smoothing average. Alternatively, the previously recorded measured values can also be smoothed with other means. The previously recorded measured values are stored as data points of a smoothed measurement profile V0 in the data memory of the control device 8.

[0075] The measurement profile V0 shows here purely by way of example in tw=15 min a turning point between an accelerating and then slowing decrease in the average brightness h.sub.avg.

[0076] In a step S7, the control device 8 will calculate the differential profile of the first order V1 as a first differential quotient of the measurement profile V0. The time instant of the minimum of the differential profile of the first order V1 corresponds to the time instant tw of the measurement profile V0.

[0077] In a step S8, the differential profile of the first order V1 is evaluated or determined to ascertain whether its minimum is reached or has been reached (“t≥tw?”. If not (“N”), a move is made back to step S3, possibly after a waiting time, which is determined by the currently set measurement rate.

[0078] If the time instant tw is reached or has been reached (“Y”), at least one action is triggered in step S9 by means of the control device 8, e.g. the heating apparatus 3 is switched off and an acoustic signal is output. The heat treatment cycle is then ended.

[0079] It may be the case that the time instant tw cannot be determined precisely, e.g. because no predictive method is used to determine the time instant tw, the measurement rate of the measurements is endless, etc. However, this is typically not critical, if the time instant lies within a time range tw−sw1≤t≤tw+sw1, since the target level of browning is then usually graded or assessed as still very good by a typical user. Generally sw1=sw2 applies, here e.g. with sw1=sw2=1 min.

[0080] It is also possible not to query the achievement of the time instant tw in step S8, but the time instant tw plus a time offset Δt with Δt>0 or Δt<0. In the case Δt<0, this is possible in particular by using predictive methods.

[0081] The present invention is naturally restricted to the exemplary embodiment shown.

[0082] Instead of the differential profile of the first order V1 the differential profile of the second order V2 can be used to determine the time instant tw. Use is made here of the fact that the turning point of the differential profile of the second order V2 between an accelerating and a subsequently slowing increase in this profile corresponds to the time instant tw of the measurement profile V0. In particular, a zero-crossing determination can be used to determine the time instant of the turning point of the differential profile of the second order V2.

[0083] A color saturation can also be evaluated instead of or in addition to an evaluation of a brightness.

[0084] In general, “a”, “one” etc. can be regarded as a singular or a plurality, in particular in the sense of “at least one” or “one or more” etc., as long as this is not explicitly excluded, e.g. by the expression “precisely one” etc.

LIST OF REFERENCE SIGNS

[0085] 1 oven [0086] 2 cooking chamber [0087] 3 heating device [0088] 5 oven muffle [0089] 6 LED [0090] 7 camera [0091] 8 control device [0092] B baking tray [0093] F field of view [0094] G food product [0095] havg averaged brightness value [0096] S dish [0097] S1-S9 method steps [0098] sw1 lower threshold value [0099] sw2 upper threshold value [0100] t time since start of a heat treatment cycle [0101] tw time instant of a turning point of the measurement profile VO [0102] V0 measurement profile [0103] V1 differential profile of the first order [0104] V2 differential profile of the first order