Food processing device

Abstract

A food processing device is disclosed comprising a drive assembly comprising a motor and a drive shaft connected to the motor, and comprising a food processing tool attached to the drive shaft so as, in use, to extend into a food processing container for processing food ingredients. A sensor configured to measure a characteristic of the drive assembly and generate a signal indicative of that characteristic is provided in the device. A processor is also provided in the device configured to identify a repeated variation in the characteristic relative to a moving average of the characteristic based on the signal received from the sensor, and to control the food processing device based on that identification.

Description

[0001] "FOOD PROCESSING DEVICE"

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a food processing device and to a method for controlling the same.

[0004] BACKGROUND

[0005] Food processing devices, including, for example, stand mixers (also known as kitchen machines) can be called on to exert relatively large forces for extended periods of time, particularly when, for example, processing dough for the making of bread, pizza, cakes, or similar materials. This processing is typically carried out using a removably-attachable food processing tool such as a dough-hook, paddle, blade, auger, or similar rotary motor-driven tool. This may be driven from below (as in a blender) or from above (as in a hand-mixer or stand-mixer).

[0006] However, certain elements of manual processing can be hard to replicate using motor-driven appliances. This includes the determination of how food processing should be varied over time, and when it should be carried out so as to avoid overprocessing or under-processing, and how and when to communicate a status of the food to a user. Finding a solution for more efficient and effective use of motor power to provide convenient and effective food processing to the user is therefore desirable.

[0007] One known way of controlling a food processing device is using a Proportionalintegral-derivative (PID) controller, or a similar controller using a closed-loop motor control algorithm, to control a food processing device motor to operate at a continuous speed selected by a user despite changes in the motor-load by automatically varying a voltage / current applied to the motor. However, these are not capable of acting to predict motor load changes before they even occur, or compensating well for periodic variations in motor-load.

[0008] A proposed solution of the prior art is to use a derivative of a moving average of the current drawn by the motor to determine the status of the food being processed. However, this suffers from the draw-back that the moving average smooths out and supresses periodic variations during processing, meaning that the system cannot adapt for them.

[0009] Periodic variations in motor load in a food processing device can cause a positively-reinforced rocking, either of the machine relative to the surface it is on, or of components of the machine relative to the base of the machine. For example, in stand mixers acting on a heavy load of dough, a side-to-side flexing of the head of the stand mixer relative to the stand and / or base can be observed. This is unsightly, noisy, and can result in fatigue (e.g., metal-fatigue) of components that are repeatedly flexed. Adding metal reinforcing elements (e.g., bumpers) to the structure of the device can suppress this flexing, but results in greater weight and expense, and is relatively ineffective against vibrations that transmit through them.

[0010] The present invention aims to at least partially ameliorate the above-described problems of the prior art.

[0011] SUMMARY OF THE INVENTION

[0012] In an aspect of the invention, a food processing device is disclosed comprising a drive assembly comprising a motor and a drive shaft connected to the motor, and comprising a food processing tool attached to the drive shaft so as, in use, to extend into a food processing container for processing food ingredients therein. A sensor configured to measure a characteristic of the drive assembly is provided, and generates a signal indicative of that characteristic. A processor is provided configured to identify a repeated variation in the characteristic relative to a moving average of the characteristic based on the signal received from the sensor, and to control the food processing device based on that identification.

[0013] In this way periodic variations relative to a rolling average can be detected and accounted for by the food processing device.

[0014] Preferably, the characteristic is at least one of:

[0015] - torque acting on the drive assembly,

[0016] - speed of the drive assembly.

[0017] Either of these can be a useful measure by which the status of the drive assembly can be assessed.

[0018] Optionally the processor is configured to control the food processing device to do at least one of: a) control a user interface to send a device-status indication to the user, b) control a user interface to display an ingredient-type indication to the user, c) control a user interface to display a food processing tool-type indication to the user, d) control a wireless communication module of the food processing device to send a wireless signal to a device-status indication to an external electronic device, e) control the motor to stop, f) control the motor to vary speed, g) control the motor to continue operating until the repeated variation ceases, h) control a heating or cooling element of the food processing device to vary the temperature of the container.

[0019] These all can provide convenience and enhanced functionality to the user.

[0020] Optionally, repetition of the periodic variation has a frequency determined by a period of rotation of the food processing tool within the food processing container. This can have the advantage of allowing the identification of a repeated interaction by the food processing tool with food.

[0021] Preferably, the periodic variation has a frequency of at least 1 Hz, and preferably between 1 Hz and 50 Hz. These correspond to typical operation frequencies of rotation of the drive assembly and allow repeated impacts of the tool to be identified.

[0022] Preferably, the processor is configured to identify repeated variation using a Periodic Disturbance Rejection algorithm. This can allow quick and accurate identification.

[0023] Optionally, the processor comprises an averaging module configured to obtain the moving average of the characteristic, and a band-stop filter configured to generate a disturbance signal in dependence on a difference between the moving average and the characteristic. The processor is configured to generate a control signal based on the disturbance signal for controlling the food processing device. This can allow compensation for short-period periodic variations.

[0024] Preferably the control signal is generated based on a derivative of the disturbance signal. This can enhance the predictive control of the food processing device.

[0025] Optionally, the control signal is a compensation signal, and the processor further comprises a long-period variation controller configured for generating a long- period variation control signal based on a sensed long-period variation, and the processor is configured to add the compensation signal to the long-period variation control signal to obtain a true control signal for long-period variations. Preferably the true control signal is a motor-control signal, and preferably a voltage applied to the motor. In this way the motor can be controlled to suppress the periodic variation at least partially.

[0026] Preferably the motor-control signal is a voltage applied to the motor, and the compensation signal is limited to be no more than between 5% and 50% of a maximum voltage applicable by the processor to the motor. In this way excessive voltage can be avoided.

[0027] Optionally, the long-period variation has frequency of less than 1 Hz.

[0028] Preferably the band-stop fdter comprises a low-pass fdter configured to exclude high-frequency noise, preferably one configured to exclude noise having a frequency multiple of the expected maximum resulting from the characteristic due to an expected normal operation of the device, more preferably 10 times the expected maximum. In this way noise can be reduced and control enhanced.

[0029] Preferably, the averaging module comprises a buffer having at least 5 slots, and preferably between 5 and 100 slots.

[0030] In another aspect of the invention, a method for controlling a food processing device is disclosed comprising steps of:

[0031] (i) providing a food processing device having a drive assembly comprising a motor and a drive shaft connected to the motor, a food processing tool attached to the drive shaft so as, in use, to extend into a food processing container for processing food ingredients therein,

[0032] (ii) measuring a characteristic of the drive assembly, and generating a signal based on the measured characteristic,

[0033] (iii) calculating a moving average of the characteristic,

[0034] (iv) identifying a periodic variation in the characteristic relative to the moving average,

[0035] (v) controlling the food processing device based on the identification.

[0036] Preferably step (iv) comprises applying a periodic disturbance algorithm to the measured characteristic.

[0037] In another aspect of the invention, a stand mixer is disclosed comprising a head unit and a stand unit hingedly attached thereto, and further comprising a mechanical damper positioned therebetween. In this way, when the head of the stand mixer is hinged downwards towards the stand section movement therebetween and vibration transmission therebetween is reduced.

[0038] Preferably the mechanical damper is a pad made of a resilient material, preferably a synthetic or natural rubber.

[0039] In another aspect of the invention, a household appliance such as, for example, a washing machine or kitchen appliance is disclosed comprising a drive assembly comprising a motor and a drive shaft connected to the motor, and comprising a tool driven by to the drive shaft so as, in use, to carry out work. A sensor configured to measure a characteristic of the drive assembly is provided, and generates a signal indicative of that characteristic. A processor is provided configured to identify a repeated variation in the characteristic based on the signal received from the sensor, and to control the household appliance based on that identification.

[0040] Any apparatus feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure, such as a suitably programmed processor and associated memory.

[0041] Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and / or all features in one aspect can be applied to any, some and / or all features in any other aspect, in any appropriate combination.

[0042] Whilst the invention has been described in the field of domestic food processing and preparation machines, it can also be implemented in any field of use where efficient, effective and convenient preparation and / or processing of material is desired, either on an industrial scale and / or in small amounts. The field of use includes the preparation and / or processing of: chemicals; paints; building materials; clothing materials; agricultural and / or veterinary feeds and / or treatments, including fertilisers, grain and other agricultural and / or veterinary products; oils; fuels; dyes; cosmetics; plastics; tars; finishes; waxes; varnishes; beverages; solders; alloys; effluent; and / or other substances, and any reference to “food” herein may be replaced by such working mediums.

[0043] The invention described here may be used in any kitchen appliance and / or as a stand-alone device. This includes any domestic food-processing and / or preparation machine, including both top-driven machines (e.g. stand-mixers) and bottom- driven machines (e.g. blenders). It may be implemented in heated and / or cooled machines. It may be used in a machine that is built-in to a work-top or work surface, or in a stand-alone device. The invention can also be provided as a stand-alone device.

[0044] “Food processing” as described herein should be taken to encompass chopping, whisking, stirring, kneading, mincing, grinding, shaping, shredding, grating, cooking, freezing, making ice-cream, juicing (centrifugally or with a scroll), or other food-processing activities involving the physical and / or chemical transformation of food and / or beverage material by mechanical, chemical, and / or thermal means. “Food processing attachment” encompasses any attachable component configured, for example on rotation and / or energising, to carry out any of the previously described food processing tasks.

[0045] BRIEF DESCRIPTION OF DRAWINGS

[0046] One or more aspects will now be described, by way of example only and with reference to the accompanying drawings having like-reference numerals, in which: Fig. 1 is a side-on schematic drawing of a food processing device according to an embodiment of the invention;

[0047] Fig. 2 is a top-down drawing of the container of the food processing device of Fig. 1 in plan;

[0048] Fig. 3a is a graph portraying a sensed compound characteristic of the food processing device of Fig. 1;

[0049] Fig. 3b is a graph portraying a signal component of the compound characteristic of Fig. 3a;

[0050] Fig. 3c is a graph portraying another signal component of the compound characteristic of Fig. 3 a;

[0051] Fig. 4 is a schematic diagram showing the operation of an algorithm operating on a processor of the food processing device of Fig. 1 ;

[0052] Fig. 5 is a schematic diagram showing operation of a filter of the processor of Fig. 4;

[0053] Fig. 6a is a graph showing operation of a low-pass filter of the processor of Fig. 4; and,

[0054] Fig. 6b is a graph showing operation of a notch filter of the processor Fig. 4.

[0055] SPECIFIC DESCRIPTION Fig. 1 depicts an exemplary food processing device 100 according to the invention. In this case the food processing device 100 is a stand mixer (also known as a kitchen machine) though it should be understood that the present invention is equally applicable to other food preparation devices. The term “food processing device” should be understood herein as also encompassing beverage preparation devices.

[0056] The food processing device 100 has a horizontally-extending base 110 forming a container attachment point at one end to which a bowl 200 having carryinghandles 201 can be attached. A stand section 120 extends vertically from an end of the base 110 opposite to that on which the bowl 200 is located. The stand section 120 is connected by a hinge 121 to a head section 130 supported by the stand section 120. The head section 130 extends horizontally away from the stand section 120, back along the horizontal direction of extension of the base 110, and supports on a lower surface a drive outlet 140 overhanging the bowl 200. The hinge 121 allows the head section 130 to be lifted away from, and lowered down towards, the bowl 200 when it is located on the base 110, such that a tool 150 removably attachable to the drive outlet 140 is removed from and inserted into the bowl 200 by upward and downward movement respectively.

[0057] To suppress vibration and movement between the head 130 and the stand 120, particularly relative pivoting side-to-side therebetween about the hinge 121, a mechanical damper 122 is located therebetween. This damper 122 is preferably made of a vibration-damping, resilient material such as a flexible polymer such as, for example, artificial rubber. The damper 122 may be fixed (e.g., glue on) to either or both of the head 130 or the stand 120. Alternatively, the damper 122 may be removably attachable to one or both of the head 130 and stand 120 using, for example, clips or ties.

[0058] The drive outlet 140 is preferably a planetary drive outlet, that is, a drive outlet which drives the tool 150 to rotate about its own central axis (denoted by line Y-Y in Fig. 1) and also drives the tool 150 (which is attached off-centre to the drive outlet 140) to simultaneously orbit a centre of the drive outlet 140 (denoted by line X-X in Fig. 1 that is offset but parallel to line Y-Y). To achieve this, the food processing appliance 100 imparts rotary drive impetus to the drive outlet 140 from a motor 160 via suitable gearing 170 (e.g., a sun-gear arrangement). The motor 160 may be located directly above the drive outlet 140 as depicted in Fig. 1, or it may be located in the stand section 120 with suitable drive transmission (e.g., a beltdrive or gear-train) provided to transmit drive to the drive outlet 140. Power is provided to the motor 160 either by a cable that attaches to the mains electricity, or via batteries provided with the food processing device 100.

[0059] In order for the user to control the operation of the food processing device 100, a user interface 180 is provided on the stand section 120. The user interface 180 may be a control knob, a touch-screen interface, or other form of user interface capable of receiving user instructions and providing feedback to the user. A control module 190 is also provided in the food processing device 100, for example in the stand section 120, in electronic communication with the motor 160, and the user interface 180, and with any other electronic components of the food processing device 100, for receiving feedback from them (including sensor data) and sending control signals to them. The control module 190 can include a suitable memory on which algorithms and routines can be stored, including motor-control algorithms and routines, and a suitable processing chip for carrying out those algorithms and routines. The control module 190 may also include a wireless communication module for communicating with mobile devices and external servers, including, for example, a suitable device-control app running on a user’s mobile device. The control module 190 may include a general-purpose programmable processor and memory, or it may comprise only components arranged on a printed circuit board (PCB) to carry out specific pre-arranged routines and algorithms.

[0060] To permit operation of the motor 160 to drive the tool 150 only when the head section 130 is lowered towards the stand section 120, hinging about hinge 121, a push-rod 131 is provided that actuates an interlock switch in the stand section (not shown). The control module 190 communicates electronically with the interlock switch and allows the motor 160 to be energised only when the switch is actuated.

[0061] The food processing device 100 may include heating and / or cooling elements, for example in the base section 110, to heat and / or cool the contents of the bowl 200 when it is attached to base section 110. Heating and / or cooling may be controlled using the user interface 160 to achieve a desired temperature, and automatically according to a routine / algorithm by the control module 190.

[0062] A sensor 161 is provided in electronic communication with the control module 190 for providing sensor feedback to it. The sensor 161 is associated with the drive outlet 140 and / or the tool 150 and / or the motor 161 and / or the gearing 170 (collectively the “drive assembly”) in order to sense a characteristic of its operation. The sensor 161 is preferably a speed-sensor (e.g., a Hall sensor sensing the varying magnetic field of an 8-pole ring magnet mounted on a drive-shaft of the motor as it rotates) sensing a speed of rotating of any part of the drive assembly. Sensing the speed directly is particularly advantageous as it can be done cheaply, simply, and most directly represents the present behaviour of the drive assembly, compared to other characteristics that are proportionate to speed but which will not always represent the true speed (e.g., current drawn by the motor). Alternatively, it could be a sensor measuring another characteristic, such as a torque sensor sensing torque (i.e., twisting force) acting on a part of the drive assembly. An example of such a torque sensor would be a non-contact strain-gauge sensor.

[0063] Fig. 2 illustrates an operating scenario of the food processing device 100, where dough being processed in the bowl 200 by the tool 150 as it is driven around the circular path r has formed into a lump or ball. Repeated collision by the tool 150 with the dough, located as it is only at one part of the circular path r of the tool 150 as it orbits the centre of rotation x-x of the drive outlet 140, results in a periodic variation in operating characteristics of the food processing device 100. Both the bowl 200 and the tool 150 are preferably dishwasher machine- washable, and made of a food-safe material, such as, for example, stainless steel.

[0064] The speed sensed by the sensor 161 may periodically vary as a result of the repeated collision of the tool 150 with the dough. This may be a rotary speed of any element of the drive assembly, including the tool 150 either about its own axis y-y or about the axis of rotation of the drive outlet 140 x-x. Feedback related to this characteristic is transmitted by the sensor 161 to the control module 190.

[0065] Figs. 3a to 3c illustrate graphs depicting feedback related to a varied characteristic (in this case, the speed of the motor 160) over time as sensed by the sensor 161 during operation of the food processing machine 100 on dough as depicted in Fig. 2. On the Y-axis they show the variation in the speed of rotation W of a drive-shaft of the motor 160 sensed with a Hall-sensor in revolutions per minute (RPM). The speed shown in Figs. 3a and 3b is absolute speed, whilst that in Fig. 3c shows speed variation relative to a longer-term average speed. On the X- axis they show time t elapsed in mixing in seconds. Fig. 3a shows the compound signal 300 received by the control module 190, which is made of the sum of two components - a long-period component 301 and a short-period repeating signal component 302.

[0066] As shown in Fig. 3b, the long-period component 301 of the compound signal 300 is a long-term variation (e.g., minutes-scale) and relatively large in amplitude. The long-period component 301 shows a speed that is a slower at the start, followed by a relatively rapid (e.g., tens of seconds-scale) increase, and then a relatively slow decrease (tens of seconds to minutes-scale) asymptotic to a particular speed value (e.g., a speed selected by the user using user interface 180). The motor 160 may be controlled to carry out this kind of long-period speed variation by the control module 190, or it may simply be an over-shoot of the target speed by the motor 160 or other such unintentional long-period variation.

[0067] As shown in Fig. 3c, the short-period variation component 302 of the compound signal 300 consists of a short-period (e.g., seconds-scale or less) variation in speed relative to a longer-term average. The short-period component 302 is both higher frequency and lower amplitude than the long-period component 301 and as such it is difficult for a traditional low-pass filtered PID controller to adapt speed-control to compensate for it whilst still compensating for the long-period variation, since the short-period variations are effectively swamped by the larger-amplitude long- period variations. This short-period variation is undesired as it can result in unpleasant noise and vibration, and results from the repeated interaction of the tool 150 with the dough in the bowl 200 as already described above with reference to Fig. 2.

[0068] In order to suppress the short-period, lower amplitude speed variation component 302, the control module 190 applies the periodic disturbance rejection (PDR) algorithm 400 shown in Fig. 4 to its speed control.

[0069] In the PDR algorithm 400, an error signal e representing a low-frequency, high- amplitude variation in speed relative to a target speed is generated as an input for controller C (which may be a PID controller or other suitable controller) at summing point 401. The summing point 401 generates the error signal e by subtracting the target speed w’ set on, e.g., the user interface 180, from a filtered speed signal (Wq- ) . (Wq- is generated by filter F by applying a filter to the measured speed signal W to remove high-frequency variations. The filter F may, for example, filter out frequencies higher than a frequency that is between 100 Hz and 1000 Hz, and preferably approximately 500 Hz. It can filter out the high- frequency variations by applying gain of 1 to frequencies lower than 1 / 1 Oth of the filtered frequencies (e.g., to frequencies lower than 10-100 Hz, and preferably 50 Hz), and a gain of 0.01 at the filtered frequencies. The gain may decline gradually from the frequencies to which a gain of 1 is applied to the filtered frequencies, resulting in a steadily increasing degree of filtering. The controller C then generates a duty-cycle control signal v’ to compensate for the low-frequency error signal e by, for example, modulating a voltage supplied to the motor control P. In this way the controller C can compensate for long-period speed variations such as the long- period speed variation component 301, without this control being affected by noise in the measured speed W.

[0070] To adapt for the typically short-period, lower-amplitude, periodic variations 302, an additional process is required. This is provided by short-period variation compensator 402 shown in dotted line. The short-period variation compensator 402 has as its input the measured speed W, and has a filter H and a compensator R.

[0071] As shown in Fig. 5, the measured speed W is received by an averaging module A equipped with a sampler for sampling the value of W at a particular frequency and a buffer having a number of slots, for example at least 5 slots, and preferably between 5 and 100 slots, for temporarily storing and then discarding the sampled values, and producing a moving average across the sampled values. This results in a moving average of the measured speed WAV for a previous time period (e.g., 1 second). This moving average WAV is then used to tune a notch filter (or similar band-stop filter) N which filters out the signal from the measured speed W within a narrow frequency band.

[0072] Operation of the notch filter N is portrayed in the graphs of Figs. 6a and 6b, which portray frequency f in hertz along the X axis and signal gain on the Y axis. Frequency here is representative of, for example, a frequency of the variation of the magnetic field sensed by a hall sensor used as the sensor 161. Fig. 6a shows the signal with a standard low-pass filter applied that filters out higher-frequency signals by applying a declining amount of gain as frequencies increase after a frequency fL. The short-period variation compensator 402 may include such a filter to avoid its output being affected by high-frequency noise. Fig. 6b shows a lower band of frequency than fL, in which the notch filter has been applied to the signal W at frequency fP, which is based on the moving average of speed WAV, and the gain for signals at that frequency greatly reduced, with signals outside that frequency having higher gain applied. This results in a disturbance signal d being generated by the notch filter. An expected value for fP can be between 1 Hz and 50 Hz, corresponding to the expected time that the tool 150 completes a rotation around the bowl 200. As a result of the high or low gain applied to the disturbance signal d, variations in speed relative to WAV, and which represent significant periodic variations in speed, are compensated for. The frequency band centred on fp representing a speed band centred on WAV, may have a width of between 1Hz and 50 Hz. The notch filter N may apply a gain of 0.01 to 0.0001 within the band centred on fp.

[0073] Compensator R identifies a repeated periodic variation based on the disturbance signal d. For example, compensator R can include a buffer having 5 or more slots in which values of d periodically sampled by a sampler are stored, and may identify repeated, regular variances in speed relative to the moving average in speed and compensate for them predictively. Based on the disturbance signal d, the compensator R generates a compensation signal v” of a value that will counter-act and reduce the detected periodic variation. A minimum amplitude of d may be set below which the compensator R does not compensate, or no minimum may be set. In order to predictively detect and prevent changes in speed of the motor 160 before they would otherwise occur, the disturbance signal d is subjected to signal processing. This signal processing may include the generation of a first-order derivative of the disturbance signal d. Generating a first-order derivative of d, which is proportionate to the speed of the motor, means effectively generating a signal proportionate to acceleration of the motor, that is to say a signal proportionate to a second-order derivative of the displacement of the motor. As this represents the acceleration of the motor, it can be used to predict an eventual speed if the acceleration continues. Higher-order derivatives can be generated where appropriate. The compensation signal v” can then be then generated based on this derivative. For example, the derivative can be amplified by a negative gain to counter-act the increased speed, preferably one in the range -0.01 to -0.0001, when the value of d is beyond a certain value (e.g., higher than 5 RPM, or even higher than 500 RPM depending on the task being carried out), with the gain otherwise being zero so that no compensation signal v” is produced.

[0074] Other alternative or additional options for signal processing by the compensator R to produce the compensation signal v” include measuring a period and amplitude between peaks in the disturbance signal d, and generating the compensation signal v” at a frequency and amplitude configured to counter-act the periodic disturbance. For example, the compensation signal v” may be generated at the same frequency as that of the occurrence of the peaks in the disturbance, with an equal but opposite amplitude to it, and potentially with an off-set to compensate for time-lag in sensing the disturbance. An example of this would be the detection of a periodic deceleration matching the rotation of the tool 150 about the bowl 200, indicating a repeated impact between the tool 150 and food being processed - in this circumstance the compensator R would generate an output increasing motor speed with the same frequency. Again, rather than waiting for the periodic disturbance to re-occur before counter-acting it, it pre-empts it.

[0075] A maximum value of the compensation signal v” is preferably limited to be between 5% and 50% of a maximum voltage that can be applied to the motor. In this way excessive loads can be avoided.

[0076] The compensation signal v” is then added or subtracted from the duty-cycle control signal v’ at point 403 to obtain a true control signal v. For example, if v’ is a duty-cycle that will result in excessive speed of the motor, v” will be a negative voltage that will compensate for the excessive speed. Both v and v’ may be dimensionless signals representing the percentage of the maximum voltage that has to be supplied to the motor by the motor control P.

[0077] The true control signal v is then applied to the motor control P (e.g., it modulates the voltage supplied to the motor) and compensates at least partly for the periodic variation. The motor control P then causes the motor 160 to vary its speed, generating a torque tm applied to the dough in the bowl 200. This results in a resistive torque tl, which at point 404 creates a resulting torque t that acts on the drive shaft G of the motor 160 which is then sensed to rotate at a resulting speed Wr.

[0078] Whilst the identification of a periodic variation in the characteristic of the drive assembly according to the algorithm 400 has been described as being used to control a speed on the motor 160, the algorithm 400 could additionally or alternatively act to control the food processing device 100 in different ways. Since the appearance of the periodic variation is caused by an asymmetric load on the motor 160 during each rotation of the tool 150 around the bowl 200, it may be taken as indicative of a state of the food being processed therein.

[0079] Example of foods that may form an asymmetric load include dough which has formed in to a ball, ice-cream that has formed in to a solid lump under the effect of a cooling element, chocolate that has not yet been melted under the influence of a heating element, icing sugar that has not yet been mixed to form a smooth consistency, and meringue that has not been mixed properly. With a different tool 150 attached, e.g. a food processing attachment such as a slicer or grinder, yet further things may be indicated by the appearance of the periodic variation, including repeated slicing of an object by a rotating slicing blade, grinding of coffee using a burr-grinder, asymmetric grinding of meat by a meat-grinder auger, asymmetric juicing of fruit by an auger-juicer, etc. In each case, depending on the food being processed, the appearance of the asymmetric load may indicate a particular status of the food. The control module 190 can have the food being processed identified to it by a user input, by identification of the food-specific tool 150 attached to it (e.g., where a dough-hook is attached, the food being processed is likely dough), or by a suitable sensor (e.g., a camera associated with suitable image-recognition software, or a chromatograph associated with pre-stored chemical profiles of food etc.). The food may even be identified, partly or entirely, from the periodic variation of the characteristic where is matches a particular consistency of a particular ingredient, and this identity may be displayed to the user.

[0080] Based on the food, the control module 190 may communicate a specific status of the food to the user using either the user interface 180 or via an app on a mobile device associated with the user with which the control module 190 is in wireless communication. For example, the disappearance of the periodic variation may indicate that the food being processed has reached a smooth consistency and as such is now ready, and the motor 160 may even be stopped at that point to avoid over-processing. In another example the periodic variation may indicate that further processing is needed, with the processing continuing until the periodic variation is no longer detected. Alternatively, the control module 190 may vary a temperature of the bowl 200, for example by heating to melt a lump detected within the food being mixed.

[0081] The periodic variation may also indicate something about the status of the food processing device 100 itself, or the tool 150 attached to it. For example, it may indicate that the wrong tool 150 is attached, or the lack of such a periodic variation may indicate that the food is not being processed by the tool 150. In this case the control module 190 may inform the user of this as described above.

[0082] Whilst the above food processing device 100 has been described as a stand mixer, the core principle of the invention can be applied to other devices, including beverage makers, coffee-grinders, ice-cream-makers, food processors, hand mixers, hand blenders, cooking food processors etc. Indeed, other household appliances, particularly those involving an asymmetric load (e.g., washing machines) may also benefit from this invention. Washing machines are an example of a machine in which asymmetric load generating noise / vibrations are a problem as clothes being washed can also form a “lump” periodically encountered by the ribs of the washing-machine-drum similar to that already discussed above.

[0083] It will be recognised that the above-described identification of the periodic variation relative to a moving average is advantageous compared to prior art solutions as the system may respond quickly to periodic variations without them being masked or over-ridden by longer-term, higher-amplitude variations.

[0084] As used herein, the term "removable attachment" (and similar terms such as “removably attachable”), as used in relation to an attachment between a first object and a second object, preferably connotes that the first object is attached to the second object and can be detached (and preferably re-attached, detached again, and so on, repetitively), and / or that the first object may be removed from the second object without damaging the first object or the second object; more preferably the term connotes that the first object may be re-attached to the second object without damaging the first object or the second object, and / or that the first object may be removed from (and optionally also re-attached to) the second object by hand and / or without the use of tools (e.g. screwdrivers, spanners, etc.). Mechanisms such as a snap-fit, a bayonet attachment, and a hand-rotatable locking nut may be used in this regard.

[0085] “Food safe” in this context means any substance that does not shed substances harmful to human health in clinically significant quantities if ingested. For example, it should be BPA-free. “Dishwasher safe” means that it should be physically and chemically stable during prolonged exposure to the conditions prevailing within a dishwasher machine. For example, it should be able to withstand exposure to a mixture of water and a typical dishwasher substance (e.g., washing with FairyTM or FinishTM dishwasher tablets and water, at temperatures of 82 degrees centigrade for as long as 8 hours without visibly degrading (e.g., cracking)).

[0086] It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

[0087] Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

[0088] Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

CLAIMS1. A food processing device (100) comprising:- a drive assembly comprising a motor (160) and a drive shaft connected to the motor (160), and comprising a food processing tool (150) attached to the drive shaft so as, in use, to extend into a food processing container (200) for processing food ingredients therein,- a sensor (161) configured to measure a characteristic of the drive assembly, and generate a signal (300) indicative of that characteristic,- a processor ( 190) configured to identify a repeated variation in the characteristic relative to a moving average of the characteristic based on the signal received from the sensor (161), and to control the food processing device (100) based on that identification.

2. The food processing device of claim 1, wherein the characteristic is at least one of:- torque acting on the drive assembly,- speed (W) of the drive assembly.

3. The food processing device of any preceding claim, wherein the processor (190) is configured to control the food processing device (100) to do at least one of: a) control a user interface (180) to send a device-status indication to the user, b) control a user interface to display an ingredient-type indication to the user, c) control a user interface to display a food processing tool-type indication to the user, d) control a wireless communication module of the food processing device to send a wireless signal to a device-status indication to an external electronic device, e) control the motor to stop, f) control the motor to vary speed, g) control the motor to continue operating until the repeated variation ceases, h) control a heating or cooling element of the food processing device to vary the temperature of the container.

4. The food processing device of any preceding claim, wherein repetition of the periodic variation has a frequency determined by a period of rotation of the food processing tool within the food processing container.

5. The food processing device of claiml, wherein the processor comprises anaveraging module (A) configured to obtain the moving average of the characteristic, and a band-stop filter (N) configured to generate a disturbance signal in dependence on a difference between the characteristic and the moving average, and the processor is configured to generate a control signal based on the disturbance signal (d) for controlling the food processing device, preferably wherein, the control signal is generated based on a derivative of the disturbance signal.

6. The food processing device of claim 5, wherein the control signal is a compensation signal, and the processor further comprises a long-period variation controller configured for generating a long-period variation control signal based on a sensed long-period variation, and the processor is configured to add the compensation signal to the long-period variation control signal to obtain a true control signal.

7. The food processing device of claim 6, wherein the true control signal is a motor-control signal (V), preferably a voltage applied to the motor.

8. The food processing device of any one of claims 5-7, wherein the band-stop filter comprises a low-pass filter configured to exclude high-frequency noise, preferably one configured to exclude noise having a frequency a multiple of the expected maximum resulting from the characteristic due to an expected normal operation of the device, more preferably 10 times the expected maximum.

9. A method for controlling a food processing device comprising steps of:(i) providing a food processing device having a drive assembly comprising a motor and a drive shaft connected to the motor, a food processing tool attached to the drive shaft so as, in use, to extend into a food processing container for processing food ingredients therein,(ii) measuring a characteristic of the drive assembly, and generating a signal based on the measured characteristic,(iii) calculating a moving average of the characteristic,(iv) identifying a periodic variation in the characteristic relative to the moving average,(v) controlling the food processing device based on the identification.

10. The method of claim 9, wherein step (iv) comprises applying a periodic disturbance algorithm to the measured characteristic.

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