Hair styling device

Abstract

Hair styling device comprising at least one heat generating element; a power supply input configured for receiving input power for powering the at least one heat generating element; a power electronics circuitry configured to power the at least one heat generating element with a configurable heating power by gating the input power based on at least one driving signal; and a controller configured to generate the at least one driving signal.

Description

HAIR STYLING DEVICEField of the Invention

[0001] The present invention generally relates to a hair styling device, in particular to a professional hair styling device for use in a hairdressing salon, comprising a heat generation control mechanism, as well as to a method for controlling at least one heat generating element in a hair styling device.Background of the Invention

[0002] Hair styling devices are generally known electric devices and may be configured to blow heated air through a main body. The heated air can be directed to a person’s hair to dry and style the hair. Hair styling devices can be handheld devices, including a handle mounted substantially transversely to the main body. Other handheld hair styling devices may include a pair of movable jaws in between which hair can be clamped such that it can be styled, sometimes also referred to as hair straightening devices. Alternatively, hair styling devices may be stand-alone devices and may for example include a headset, such as hood hair dryers. Hair styling devices may come in various types, such as a personal hair styling device, for example for occasional use at home generally by a person drying and / or styling their own hair, a travel hair styling device which may for example be relatively small, lightweight and / or foldable for easy transportation, or a professional hair styling device which may be used by a person styling someone else’s hair, for example in a professional setting, used by a hairdresser in a hairdressing salon, in photo studios, before fashion shows, in education, or in any other professional context. Each of these various types of hair styling devices can include specific technical requirements due to the different use made of said type of hair styling devices.

[0003] Hair styling devices generally comprise one or more heat generating elements. Heat generating elements may also be referred to as heat elements or heating elements. Different power ratings may be applied for these heat generating elements depending on the application. Small consumer-oriented devices, such as travel hair dryers, will typically comprise smaller heating elements and have lower power ratingscompared to professional hair styling devices. A professional hair styling device usually requires that a sufficient amount of heat can be generated by the heat generating element to achieve a desired exit temperature of the air for all airflow rates.

[0004] However, it is known that in existing hair styling devices, the amount of available heat level settings is very limited. Setting the different heat levels may be achieved by switching one or more heat generating elements on or off. For example, hair styling devices are commonly equipped with two heat generating elements with a same or different power rating, to respectively create two or three possible heat modes by turning them on separately or simultaneously.

[0005] Many different hair types exist, e.g. thick hair, thin hair, hair with a dry scalp, curly hair, chemically treated hair et cetera, which can benefit from applying a different heat level or temperature level during styling. Access to a wide variety of heat levels may be required for creating different hair styles in a professional context. Therefore, it is desirable for a hair styling device to be able to apply a broad range of heat levels or temperature levels during styling.

[0006] It is therefore an object of the invention to provide a hair styling device configured to provide an extended range of heat levels. It is similarly an object of the invention to provide an energy efficient method for controlling at least one heat generating element in a hair styling device to provide an extended range of heat levels.Summary of the Invention

[0007] According to a first aspect, this object is achieved by a hair styling device according to claim 1. The hair styling device comprises at least one heat generating element, a power supply input, a power electronics circuitry and a controller. The power supply input is configured for receiving input power for powering the at least one heat generating element. The power electronics circuitry is configured to power the at least one heat generating element with a configurable heating power by gating the input power based on at least one driving signal. The controller is configured to generate the at least one driving signal with a duty cycle configured according to the configurable heating power.

[0008] A heat generating element may be one or more coiled resistance wires, e.g. when the hair styling device is a hair dryer, or may be one or more heating plates, e.g. when the hair styling device is a hair straightener. The power supply input may be a cable connected to a plug, configured to be plugged into a socket for connecting to a wall socket. The controller controls the powering of the at least one heat generating element via the power electronics circuitry, by providing the at least one driving signal. The power electronics circuitry may be configured to power the at least one heat generating element with a configurable heating power by gating the input power with or by at least one driving signal. The power electronics circuitry allows power to flow from the power supply to the at least one heat generating element by applying the at least one driving signal as a gating signal. As such, the at least one driving signal dictates when power is provided to the at least one heat generating element. The configurable heating power may also be referred to as a configurable heating power setting. The configurable heating power is determined by the controller and may depend on user settings. The configurable heating power may be configurable by a user input. A duty cycle is defined in electronics for a periodic signal as a ratio of the time that the signal is on, e.g. a pulse is present, to the period length of the signal. For example, with a duty cycle of 50%, in each period the duration of a pulse equals the duration that the signal is off. A signal that is constantly zero can be viewed as having a duty cycle of 0%. Analogously, a signal that has a constant non-zero value can be considered to have a duty cycle of 100%. The at least one driving signal is thus a periodic signal, with a duty cycle that varies over time, depending on the generation of the at least one driving signal performed by the controller. The controller is configured to configure the duty cycle, meaning that the duty cycle is configurable between 0% and 100%, enabling intermediate values of the duty cycle. As such, the configurable duty cycle may comprise at least one other value between 0% and 100%, and preferably a plurality of values between 0% and 100%. A continuous range of intermediate values may be achieved, or the range of possible duty cycles may comprise discrete values between 0% and 100%, e.g. with steps of 1 % or other steps. Optionally, the duty cycle may be configured to comprise values in smaller intervals than between 0% and 100%, e.g. between 10% and 90%, or between 0% and 50%, or in any other interval. Analogously to a configurable duty cycle, a configurable heating power can be understood as comprising at least one value, and preferably a plurality of values, between zero and a maximal heating power determined by the at least oneheat generating element, for example by a sum of the respective maximal heating powers of one or more heat generating elements. An appropriate duty cycle is determined by the controller such that the at least one driving signal, comprising the duty cycle, results in the desired configurable heating power being allowed through to the at least one heat generating element. For example, the duty cycle may be proportional to the configurable heating power.

[0009] The at least one driving signal may be modulated by the controller by applying pulse width modulation (PWM). In other words, a variable pulse width of the at least one driving signal may determine the power that is supplied to the at least one heat generating element. During a pulse of the at least one driving signal, power is allowed through to the at least one heat generating elements. The controller may determine the pulse width based on the configurable heating power. Applying PWM is a way of configuring the duty cycle and can be performed according to the configurable heating power to generate the at least one driving signal. It is noted that other modulation schemes, for example pulse amplitude modulation (PAM), may also be applied instead of pulse width modulation, however, PWM may be especially advantageous for the application of hair styling devices, at least due to the reasons set out below.

[0010] By modifying the duty cycle of the driving signal, the at least one heat generating element can be powered at intermediate values between a maximum power, i.e. when continuously letting through the power from the power supply, and no power, i.e. when the power from the power supply is not allowed through by the power electronics circuitry. At maximum power, the duty cycle is configured to be one, or correspondingly 100%, while at no power, the duty cycle is configured to be zero, or correspondingly 0%. The configurable duty cycle can enable the power to flow through the heat generating element during a percentage of time, resulting in the adjustable powering of the at least one heat generating element over a continuous range instead of step- wise. The effectively applied power is the average power corresponding to the duty cycle. By varying the duty cycle, the at least one heat generating element is essentially being powered at a fraction, corresponding to the percentage of time, of the maximum power. As such, stepless control of the heat generation is made possible, resulting in a continuous range of possible heat levels. By providing the hair styling device according to the first aspect, a continuous range of heat level settings may be provided.It is a further advantage that the configurable heating power leads to a more efficient energy usage of the hair styling device. In particular, the configurable heating power setting can be set to a value lower than the maximum power and is thus not set at a maximum power by default, even when this is not necessary.

[0011] A further advantage may be provided by the invention in that the heat generating element cools off more quickly after switching off the powering of the heat generating element compared to the cooling off time required by a traditional hair styling device. Traditional hair styling devices power their heat generating elements at full power which results in a long cooling time to reach the ambient temperature when switched off. This is due to the large temperature gradient that has to be overcome when cooling off the heating element to ambient temperature. The hair styling device according to the first aspect does not suffer from this long cooling off period because the heat generating element is only powered at an intermediate value and thus has to overcome a significantly smaller temperature gradient to reach ambient temperature. Cooling off quickly may be advantageous for the lifetime of the hair styling device, in particular for the lifetime of the housing and / or for the lifetime of the at least one heat generating element, and for preventing accidental burning of a person touching the hair styling device. Faster cooling of the heat generating element may also be advantageous for providing a so-called cold shot function, i.e. blowing cold air, by a hair dryer. During such a cold shot mode, the hair dryer only blows air, without providing heating via the heat generating element. Because the heat generating element is able to cool down quickly, the hair dryer can blow relatively cold air almost instantaneously after activation of the cold shot function, and hence can provide a well-performing cold shot function.

[0012] According to an embodiment, the power supply input is further configured for receiving alternating current, AC, input power and the controller is further configured to generate the at least one driving signal based on a periodicity of the AC input power. The periodicity of the AC input power is characterised by a period length. When the power supply input is configured to receive AC input power, it can be directly connected to an AC power supply wall socket, providing mains power from the power grid. In general, the AC input power provides a periodically alternating voltage, with a maximal and a minimal value that are equal in absolute value and that have an opposite sign.The period length is the duration of one period of the alternating voltage of the input power. It is advantageous that the controller generates the at least one driving signal based on the periodicity of the AC input power. This allows for a symmetrical loading of the at least one heat generating element. Symmetrical loading of the heat generating element means that power is supplied in balance between positive parts of periods of the AC input power and the negative parts. An integral of the applied voltage of the AC power supply over time, is then zero. Symmetrical loading is advantageous considering electromagnetic compatibility, EMC, in order to avoid disturbing the mains signal.

[0013] According to further embodiments, the hair styling device further comprises a zero-crossing detector circuitry for detecting zero-crossings of the AC input power, wherein pulses of the at least one driving signal are aligned with the zero-crossings of the AC input power. By applying zero-crossings detection for aligning the pulses with the AC input power, symmetrical loading can be safely implemented. Switching the powering on and off during zero-crossings avoids introducing undesired spikes into the power grid, further adding to the electromagnetic compatibility of the hair styling device.

[0014] According to further embodiments, the at least one driving signal has pulses characterised by a pulse width equal to K times the period length, with K a natural number larger than zero. By applying a pulse width of a number of times the period length of the AC power, symmetrical loading is ensured since equal power is allowed through during positive and negative parts of the period. Additionally, by gating the AC power for entire periods, rather than parts of a period, the power electronics circuitry can be designed and implemented more easily.

[0015] According to further embodiments, the at least one driving signal has pulses characterised by a pulse width equal to half the period length. When fixing the pulse width of pulses of the at least one driving signal, the controller may configure the duty cycle by varying the time between pulses, i.e. when the at least one driving signal is zero. This allows for an efficient implementation requiring only limited computational power of the controller. Further, the fixing of the pulse width to half of the period length is especially advantageous when combined with aligning the pulses of the at least one driving signal with the zero-crossings of the AC input power, by use of a zero-crossing detector circuitry. In that case, the pulse width of half the period length allows selectionof either positive or negative halves of the periods of the AC input power. This simplifies the further implementation of the hair styling device to comply with EMC requirements.

[0016] According to further example embodiments, the at least one driving signal has pulses characterised by a pulse width equal to Q times half the period length and has a time between pulses equal to P times half the period length, wherein P and Q are natural numbers larger than zero. In other words, the at least one driving signal is constructed using units of half the period length. For example, with Q equal to 1 , the duty cycle is 50% if P equals 1 , 33% if P equals 2, 25% if P equals 3, and so on. With Q equal to 2, the duty cycle is 67% if P equals 1 , 50% if P equals 2, 40% if P equals 3, and so on. As such, any duty cycle between 0% and 100% can be achieved or at least closely approximated. In addition, the control of the at least one heat generating element can remain synchronised with the zero-crossings of the AC input power to avoid undesired EMC behaviour.

[0017] According to further example embodiments, the at least one driving signal is periodically shifted over half the period length. By shifting the driving signal by half a period, opposite pulses of the AC input power are allowed through. By doing this at a fixed rate, i.e. periodically, the positive and negative pulses of the AC input power are balanced out over time. This may, for example, be repeatedly done after J times the period length, wherein J is a natural number larger than zero, e.g. 50, i.e. every minute for a 50 Hz net frequency. Alternatively, this may be done after a predetermined amount of pulses. This further improves the EMC behaviour of the hair styling device, e.g. to reduce flicker.

[0018] According to further embodiments, the at least one heat generating element is a plurality of N heat generating elements and the at least one driving signal is a plurality of L driving signals each having a respective configurable duty cycle. Further, the N heat generating elements are powered based on the L respective driving signals, with N a natural number larger than one and L a natural number larger than zero.

[0019] By providing L driving signals, L being larger than zero, grouping of heat generating elements is allowed. As such, groups of heat generating elements can be collectively powered as a result of the gating of a single driving signal. For example, L may equal two in a hair styling device comprising three heat generating elements, i.e.N equals three for this example. The powering of a group of two heat generating elements is then controlled by a single driving signal, while the powering of the remaining heat generating element is controlled by another driving signal. Alternatively, no grouping is performed and the heat generating elements are separately powered, i.e. L may be equal to N. As another example, in the hair styling device of the previous example, L may equal three. L cannot exceed the value of N, with N being the number of heat generating elements of the hair styling device. Optionally, the L driving signals may be the same and / or comprise the same duty cycle.

[0020] By providing a plurality of heat generating elements, the desired power for heating can be divided over different heat generating elements, resulting in a faster cooling and reduced wear of the heat generating elements. In other words, a more efficient power distribution may be achieved. Smaller currents may then need to be switched for the gating of the at least one driving signal. This provides the additional advantage of reducing flicker. Additionally, more heating power can be provided by the hair styling device. Further, by providing a corresponding driving signal for each group of heat generating elements, the heat generating elements can be powered differently. For example, when L equals N, each heat generating element can even be powered separately. By providing a driving signal comprising a specific duty cycle per group of heat generating elements, the controller has more flexibility when generating the driving signals. For example, when a low heating power is required, only one heat generating element or one group of heat generating elements may be powered, while the other heat generating elements may be turned off. Advantageously, the configurable heating power may be divided over heat generating elements powered at intermediate heat levels, instead of powering selected heat generating elements at a maximal power. This may be especially beneficial for reducing wear of the heat generating elements, as well as for providing an effective cold shot function.

[0021] According to an embodiment, the power electronics circuitry comprises at least one triode for alternating current, TRIAC, gated by the at least one driving signal for powering the at least one heat generating element by gating the input power. A TRIAC is an electronic component with three terminals. The gate terminal controls the electric flow between the two remaining terminals. Here, the at least one driving signal isapplied to the gate terminal of the at least one TRIAC to allow an electric flow between the two remaining terminals.

[0022] When a pulse of the driving signal is applied to the TRIAC, a current is allowed through the two remaining terminals during both positive and negative AC input voltages. A TRIAC thus can power a heating element during a complete AC power cycle. This is an advantageous property of TRIACs that is not generally the case for other electronic components. For example, widely used thyristors do not possess this property and allow for instance only positive currents to pass through. In addition, when no signal is applied to the gate terminal of a TRIAC, no current can flow through. This increases the safety of the hair styling device, as the default (unpowered) state of the gate terminal will deactivate the heating elements.

[0023] According to further embodiments, the at least one heat generating element is a plurality of M heat generating elements, the at least one TRIAC is a plurality of M TRIACs, and the M heat generating elements are powered by the respective M TRIACs, M being a natural number larger than zero. By providing a plurality of heat generating elements, the task of generating heat is divided over multiple heat generating elements. Less heat needs to be generated by each heat generating element to achieve a same temperature. It is thus advantageous to provide a plurality of heat generating elements, as this results in a lower loading, and therefore a lower wear, of each of the heat generating elements. The TRIACs consequently also wear down slower, as they conduct less current. In addition, the heat generating elements cool down faster when switching off the powering. Further, providing a TRIAC for each heat generating element further adds to the safety of the hair styling device, because each heat generating element can be controlled separately. When a problem is detected concerning one of the heat generating elements, it can be individually switched off.

[0024] According to further embodiments, the at least one driving signal is a plurality of L different driving signals. By applying different driving signals, less power at a same frequency is loading the mains compared to a situation where all heat generating elements are powered identically at the same time. When the input power is gated equally, a large signal, resulting from all heat generating elements combined, with a same spectrum is introduced into the mains. Resonant frequencies can cause flickeror otherwise imbalance the mains. Thus, gating the M TRIACs dissimilarly reduces EMC problems, e.g. related to flicker.

[0025] According to further embodiments, the L different driving signals have different pulse widths. Applying different pulse widths is a way of generating driving signals with different duty cycles in a manner that avoids complicating the power electronics circuitry.

[0026] According to further embodiments, respective pulses of the L different driving signals are time-interleaved. By interleaving the pulses of the driving signals, the heat generating elements are powered in an alternating scheme, thereby using less power at a given moment in time. This is more efficient than applying a higher amount of power to multiple heat generating elements simultaneously, alternated by periods of time without powering.

[0027] According to an embodiment, the at least one heat generating element is a plurality of heat generating elements having a same maximum power rating. By providing heat generating elements with the same maximum power rating, the heat generating elements can be powered such that they wear down equally. An increased ease of manufacturing is a further advantage. Alternatively, providing heat generating elements having a different maximum power rating may be advantageous considering EMC requirements, e.g. to avoid flicker issues stemming from large powers having the same frequency components.

[0028] According to an embodiment, the hair styling device further comprises a main body having a back end. The main body further has a front end including an air exit. The main body is configured to guide an airflow from an air entrance to the air exit. The power electronics circuitry is placed in the airflow. As power electronics circuitries usually conduct significantly large currents, heating up of the components is a common concern. The operating temperature has an impact on the lifecycle of electronic components. By placing the power electronics circuitry in the airflow, the electronic components mounted thereon are being cooled by the air flowing along the power electronics circuitry. Additionally, the power electronics circuitry can thereby not cause unwanted heating up of the handle, which is convenient for a person holding the hair styling device.

[0029] According to further embodiments, the hair styling device further comprises a motor configured to generate the airflow, wherein the power electronics circuitry is placed between the motor and the at least one heat generating element. By placing the power electronics circuitry between the motor and the heat generating element, heat dissipated from the power electronics circuitry advantageously pre-heats the air before it reaches the heat generating element. The heat generating element then needs to perform less heating and needs less powering, resulting in a more energy efficient hair styling device.

[0030] According to embodiments, the hair styling device further comprises a temperature sensor for measuring a temperature in the hair styling device. The controller is further configured to adapt the configurable heating power based on a difference between the measured temperature and a predetermined temperature. The predetermined temperature may, for example, be configurable by a user input. By providing a feedback loop within the hair styling device, a given temperature can be held constant more precisely. In addition, a continuous range of desired temperatures can be precisely achieved.

[0031] According to further embodiments, the temperature sensor is mounted on the at least one heat generating element. The temperature sensor may preferably be mounted downstream, near an air exit. When mounting the temperature sensor on the heat generating element, the air temperature is measured right before exiting the hair styling device. Therefore, this can provide a realistic measurement of the air temperature that is emitted from the hair styling device. It is a further advantage that the temperature sensor is able to detect overheating issues of the at least one heat generating element.

[0032] According to a second aspect, the object is achieved by a method for controlling at least one heat generating element in a hair styling device. The method comprises a step of obtaining, by a controller, input power for powering the at least one heat generating element. The method further comprises a step of generating, by the controller, at least one driving signal with a duty cycle configured according to a configurable heating power. The method further comprises a step of gating, by a power electronics circuitry, the input power based on the at least one driving signal resultingin a gated power. The method further comprises a step of powering, by the power electronics circuitry, the at least one heat generating element by the gated power. The method can provide one or more of the above-mentioned advantages.Brief Description of the

[0033] Fig. 1 shows a schematic view of a first embodiment of a hair styling device comprising at least one heat generating element according to a first aspect of the invention;

[0034] Fig. 2 shows a schematic view of a second embodiment of a hair styling device comprising at least one generating element;

[0035] Fig. 3 shows three graphs of voltage over time illustrating the method for controlling at least one heat generating element in a hair styling device according to a second aspect of the invention;

[0036] Fig. 4 shows three graphs of voltage over time illustrating the method for controlling at least one heat generating element in a hair styling device according to a second aspect of the invention;

[0037] Fig. 5 shows three graphs of voltage over time illustrating the method for controlling at least one heat generating element in a hair styling device according to a second aspect of the invention;

[0038] Fig. 6 shows a schematic view of a third embodiment of a hair styling device comprising two heat generating elements;

[0039] Fig. 7 shows five graphs of voltage over time illustrating the method for controlling at least one heat generating element in a hair styling device according to a second aspect of the invention;

[0040] Fig. 8 shows five graphs of voltage over time illustrating the method for controlling at least one heat generating element in a hair styling device according to a second aspect of the invention;

[0041] Fig. 9 shows a cross-sectional view of a fourth embodiment of a hair styling device; and

[0042] Fig. 10 shows graphs of voltage over time illustrating the method for controlling at least one heat generating element in a hair styling device according to a second aspect of the invention.Detailed Description of Embodiment(s)

[0043] Figure 1 shows a schematic view of a first embodiment of a hair styling device comprising at least one heat generating element according to a first aspect of the invention. In particular, the hair styling device is a hair dryer 1 comprising a power supply input 9, shown in Figure 9, configured for receiving input power 99 via the mains 111 , i.e. the power grid. Subplot 990 illustrates an AC voltage of the input power 99 over time. The surface under a voltage curve, for example in subplot 990, is a measure for the transmitted power, for example input power 99. The hair dryer 1 comprises at least one heat generating element 13.

[0044] Heat generating elements 13 may for example be bare, coiled resistance wires, such as for instance nichrome (NiCr) wire, wrapped around an electrically insulating structure. Nichrome is a family of alloys of nickel and chromium and is a poor conductor of electrical current compared to something like copper wire. This gives the alloy enough resistance to get heat from the current flowing into it. Bare resistance wires are commonly used for heating up air to be emitted from the hair styling device, for example in a hair dryer. Alternatively, heat generating elements may include heat conducting plates, i.e. heating plates, or rods, i.e. heating rods, for instance having coiled resistance wires incorporated on the inside of said plates or rods. Heating plates are commonly included in hair straightening devices. Heating rods may for example be integrated in curling irons. Optionally, heat conducting plates or rods may be fabricated in a bent shape and coiled resistance wires can be tailored thereto configuration-wise. Heat generating elements that use a type of energy conversion process other than a coiled resistance wire may also be applicable to hair styling devices.

[0045] Returning to Figure 1 , the hair dryer 1 further comprises a power electronics circuitry 300 configured to control the power 350 for powering the at least one heat generating element 13. This is done by gating the input power 99 based on at least one driving signal 250. Subplot 2500 shows an example of a voltage of the driving signal 250 over time. The hair dryer 1 comprises a controller 200, also referred to as a controller circuitry, configured to generate the driving signal 250 by applying pulse width modulation according to a configurable heating power or heating power setting. The heating power may be configured based on a predetermined mode or may be user defined. For example, a predetermined mode may comprise a heat level that has been found to be appropriate for many hair styles. Alternatively, before use of the hair styling device, a user may provide input values from which the setting can be derived. For example, a user may operate a button, a knob, a touch screen or another input mechanism to indicate a desired heating level. For example, a button may be pushed multiple times to reach a maximal heating level in steps, e.g. after pushing 10 times. The steps may then comprise equally large increases of heat, or other types of incremental schemes. Alternatively, a button may be pressed during an amount of time, until reaching a maximal time, e.g. 5 seconds, corresponding with a maximal heating level. It is also a possibility to provide a decreasing heating level starting from the maximal heating level instead of an incremental scheme. The hair styling device may also be configured for heating the at least one heat generating element depending on the possible heat levels reached during this set-up process, such that the user can experience the possible heat levels. Using the input mechanism, a user may define heat settings for a number of corresponding heat modes, e.g. 10 different modes, between which the user can later switch, by e.g. pressing a different button, during future operation of the hair styling device, including after shutting down the hair styling device. The input power 99 is selectively turned on and off by the at least one gating signal 250, resulting in an adapted heating power 350 effectively comprising an intermediate power level. The power 350 for driving the heat generating element 13 is illustrated in subplot 3500. Subplot 3500 shows a voltage value of the power 350 over time, in accordance with the on-off switching of the input power 99 caused by the pulsed driving signal 250. It is noted that the waveforms of the voltage 350 applied to the heat generating elements 13 are not necessarily as shown throughout the figures. The figures merely show this specific waveform shape for illustrative purposes.

[0046] Figure 2 shows a schematic view of a second embodiment of a hair styling device comprising at least one generating element. In particular, Figure 2 shows a hair straightening device, comprising at least one heat generating device, e.g. two heating plates 13, which may be heated by an underlying resistance coil. Referring to Figure 2, the same reference numerals refer to the same functional components as described above with reference to Figure 1 . The at least one driving signal 250 in this case may comprise two driving signals 250 to separately drive the heating plates 13. The at least one driving signal 250 may comprise one driving signal 250 for controlling the powering of both heating plates 13 simultaneously. The controller 200 generates the driving signal 250 to comprise pulses, as shown in subplot 2500, that turn the powering via input power 99, shown in subplot 990, on and off, e.g. 50% of the time during a certain time interval. The input power 99 may originate from the mains 111. By doing so, the resulting power 350 comprises an on-off-switched version of the input power 99, as shown in subplot 3500. As such, an intermediate heat level of the heating plates 13 is reached, e.g. corresponding to half of the maximal power rating of the heating plates 13 in the case when the driving signal 250 comprises a pulse 50% of the time. By applying pulse width modulation, i.e. by generating the pulses of the driving signal 250, any intermediate heating power level can be achieved, resulting in a hair styling device being able to provide any desired heating level between zero and a heating corresponding to the maximal power rating. The concept of pulse width modulation, here advantageously applied, is further elucidated by Figure 3.

[0047] Turning to Figure 3, the principle of configuring a duty cycle of at least one driving signal for controlling heat generating elements in a hair styling device is illustrated. Subplot 301 shows a voltage, i.e. an input voltage, of an AC input power 99 over time. The AC input power 99 and the input voltage have a periodicity characterised by a period length 90, as provided by the mains. The controller 200 is further configured to generate the at least one driving signal 250, illustrated in subplot 302, based on the periodicity. The at least one driving signal 250 has pulses 50 characterised by a pulse width 400 equal to three times the period 90, i.e. in this example K equals 3 yet may be any other value larger than zero. As an example, for a duty cycle of 50%, the time between pulses is also three times the period length. Alternatively, the at least one driving signal 250 may have a pulse width equal to a fraction F, e.g. equal to 0.5 or 50%, of a period length 90 of a supply signal 99 suppliedby the mains 111. The hair styling device 1 may further comprise a zero-crossing detector circuitry for detecting zero-crossings 500 of the AC input power 99. Pulses 50 can then be advantageously aligned with the zero-crossings 500 of the AC input power 99 to enable symmetrical loading and to avoid introducing undesired spikes into the power grid 111. Subplot 303 depicts a voltage, as a function of time, of the corresponding power 350 for powering the heat generating element.

[0048] Figure 4 and Figure 5 illustrate the principle of configuring a duty cycle of at least one driving signal for controlling heat generating elements in a hair styling device, in a different implementation than shown in Figure 3. In this example, the at least one driving signal 250, shown in subplots 502, 602, has pulses 50 characterised by a pulse width 400 equal to half the period length 90. Subplots 501 , 601 show the voltage provided by the input power 99 along with the zero-crossings 500 and the period length 90 characterising the periodicity of the input voltage. Subplots 503, 603 show a voltage of the resulting heating power 350 applied to the at least one heat generating elements 13. Figure 4 and Figure 5 show the driving signal 250 for a duty cycle of 1 / 6 or 16.67%, respectively during positive and negative voltages of the AC input power 99. This is realised by setting the time between pulses 400 to 5 times half the period length 90. As another example, when the duty cycle is 1 / 2 or 50%, half of every period of the AC input power voltage will be selected by the driving signal 250. As yet a further example, when the duty cycle is 1 / 4 or 25%, half of every second period of the AC input power voltage will be selected by the driving signal 250. When the duty cycle is 1 or 100%, the driving signal 250 has a constant value, as such continuously allowing through the input power 99 to the at least one heat generating element 13. Here, the pulses of the at least one driving signal 250 are aligned with the zero-crossings of the AC input power. This allows selection of either positive or negative halves of the periods of the AC input power 99, as respectively illustrated in Figure 4 and Figure 5. During operation, the controller may switch between selecting positive and negative parts of the AC input. This can be done by periodically shifting the driving signal 250 by half the period length 90, as is done between Figure 4 and Figure 5. This can be done for any type of driving signal and may, for example, be done once per minute. Thanks to this alternation, a more symmetrical loading is achieved, which is advantageous considering EMC. When the driving signal 250 selects only parts of the period of the AC input voltage that are either positive or negative, this scheme mitigates a need forperforming an additional rectification of the current provided by the AC input power 99. A rectification, e.g. by use of a diode, is then not necessary due to the selection, performed by the driving signal 250, of current flowing in a single direction. Therefore, any electronic component that can perform a switching functionality may be used for this implementation. For example, a thyristor, a bipolar junction transistor (BJT) or a metal-oxide semiconductor field-effect transistor (MOSFET), a solid-state relays (SSR), an insulated gate bipolar transistor (IGBT) et cetera. In order to achieve duty cycles larger than 50%, parts of both positive and negative period halves of the AC input power 99 may need to be selected. Without the use of TRIACs, at least two electronic unidirectional switching components would be necessary for powering of each heat generating element: a first for conducting current during either the positive or negative period halves of the AC input power and a second for conducting current in the opposite direction. Therefore, it is especially advantageous to make use of TRIACs due to their capability to conduct current both when positive and negative voltages are applied at the remaining terminals. As such, by powering the heat generating elements with a TRIAC, less electronic components are required.

[0049] Figure 6 shows a schematic view of a third embodiment of a hair styling device comprising two heat generating elements. In particular, the hair styling device is a hair dryer 1 comprises a main body 2 having a back end 3 including an air entrance 4 and a front end 5 including an air exit 6, wherein the main body 2 is configured to guide an airflow 600 from the air entrance 4 to the air exit 6. In this example, the power electronics circuitry 300 comprises two triodes for alternating current, also called TRIACs, 301 , 302, respectively gated by two driving signals 251 , 252 for respectively controlling a power 351 , 352 of the heat generating elements 131 , 132 by gating the input power 99. The driving signals 251 , 252 may be the same for gating both TRIACs 301 , 302, or may be differently modulated driving signals 251 , 252. For example, differently modulating may be done by applying different pulse widths 401 , 402, as illustrated in Figure 7, and / or by time-interleaving pulses of the driving signals, as illustrated in Figure 8. The heat generating elements 131 , 132 may advantageously have a same maximum power rating. The hair styling device 1 may further comprise a temperature sensor 210 for measuring a temperature in the hair styling device 1 . For example, in a hair dryer, an air temperature could be measured. In a hair straightener, a temperature of the heating plate(s) may be measured. Analogously, in a hair curler,a temperature of the heating iron or rod may be measured. By measuring the temperature, different temperature levels or corresponding heat modes may be achieved. Alternatively, a temperature of a housing and / or handle of the hair styling device may be measured for safety purpose. The controller 200 may further be configured to adapt the configurable heating power based on a difference between the measured temperature and a predetermined temperature, so as to implement a feedback control loop. In this example, the temperature sensor 210 may be mounted on the main body 2, e.g. on a housing of the main body 2. Alternatively, the temperature sensor 210 may be mounted on one of the heat generating elements 131 , 132. Advantageously, the temperature sensor 210 may be positioned at an air outlet of the hair styling device to achieve a value representative of the air temperature.

[0050] Referring to Figure 7, five graphs of voltage over time are shown illustrating modulating the driving signals 251 , 252 differently by applying different pulse widths 401 , 402, for example of the hair dryer 1 of Figure 6. Subplot 701 illustrates the input power 99, comprising a periodicity characterised by the period length 90. Subplot 702 shows the driving signal 251 , comprising pulses 51 with a pulse width 401. In the example of Figure 7, the pulses 51 are separated in time by a time 403. Alternatively, the pulses 51 may be separated by a time equal to the pulse width 401 , or by another pulse width. Subplot 703 shows the driving signal 252, comprising pulses 52 with a pulse width 402. The pulses 52 are separated in time by a time 404. Alternatively, the pulses 52 may be separated by a time equal to the pulse width 402, or by another pulse width. Subplots 704, 705 respectively show the resulting power 351 , 352 applied to the respective TRIACs 301 , 302 for powering the heat generating elements 131 , 132. As shown, the pulses 51 , 52 select parts of the input power 99 that are allowed through to power the heat generating elements 131 , 132. By applying the pulses in driving signal 250, the resulting power 350 applied to the heat generating element comprises a frequency spectrum which is amended with respect to the input power 99. By switching the input power 99 off in between the pulses 50, additional frequency components are introduced and are sent back into the mains circuit 111. These frequency components may cause undesired effects, especially since the power is significantly high. For example, a heat generating element may have a power rating of 1 kilowatt, kW, which can have a significant effect on the mains 111. By applying different pulse widths, the heat generating elements 131 , 132 are not powered equallyand thus have a different frequency spectrum. When applying the same pulse widths, a combined power comprising a same frequency spectrum is loading the mains 111. However, when applying different pulse widths 401 , 402, the power 99 is separated into two powers 351 , 352 of a lower magnitude which each comprise a different frequency spectrum. Applying different pulse widths 401 , 402 is thus advantageous considering loading of the mains 111 , e.g. electromagnetic compatibility, because less power of a certain frequency spectrum is introduced into the power grid.

[0051] Figure 8 shows another five graphs of voltage over time illustrating modulating the driving signals 251 , 252 differently by applying different pulse widths 401 , 402 in a time-interleaved manner, for example of the hair dryer 1 of Figure 6. Subplot 801 illustrates the input power 99, comprising a periodicity characterised by the period length 90. Subplot 802 shows a driving signal 255, comprising pulses 55 with a pulse width 405. Subplot 803 shows a driving signal 256, comprising pulses 56 with a pulse width 406. In the example of Figure 8, time-interleaving is applied. The timeinterleaving may be achieved by separating the pulses 55 of driving signal 255 by the pulse width 406 of the other driving signal 256. Analogously, the pulses 56 of driving signal 256 are separated by the pulse width 405 of the driving signal 255. Subplots 804, 805 respectively show the resulting power 351 , 352 applied to the respective TRIACs 301 , 302 for powering the heat generating elements 131 , 132. As shown, the pulses 55, 56 select parts of the input power 99 that are allowed through to power the heat generating elements 131 , 132 in a way that the heat generating elements 131 , 132 are not powered at the same time. By doing so, less power is applied at any moment in time and silent periods are avoided. The powering is thus more equally applied over time, instead of applying larger peaks of powering. This is more easily manageable by the mains 111.

[0052] It is noted that Figures 4, 5, 7 and 8 illustrate that the at least one driving signal may have pulses characterised by a pulse width equal to Q times half the period length and may have a time between pulses equal to P times half the period length. In Figures 4 and 5, Q is 1 and P is 5, resulting in a duty cycle of 16.67%. In subplot 702 of Figure 7, Q is 4 and P is 2, resulting in a duty cycle of 67%. In subplot 703 of Figure 7, Q is 2 and P is 2, resulting in a duty cycle of 50%. In subplot 802 of Figure 8, Q is 4 and P is2, resulting in a duty cycle of 67%. In subplot 803 of Figure 8, Q is 2 and P is 4, resulting in a duty cycle of 33%.

[0053] Figure 10 shows graphs of voltage over time illustrating modulation of two driving signals to drive two respective heat generating elements, for example driving signals 251 , 252 controlling heat generating elements 131 , 132 of the hair dryer 1 of Figure 6. Figure 10 illustrates how different power settings can be achieved according to example embodiments.

[0054] Subplot 901 illustrates the input power 99, comprising a periodicity characterised by the period length 90.

[0055] Subplots 911 , 912, 913, 914, 915, 916, 917, 918, 919, 920, 921 show the powering of a first heat generating element 131 in 11 different power level settings respectively, according to example embodiments. Subplots 931 , 932, 933, 934, 935, 936, 937, 938, 939, 940, 941 show the powering of a second heat generating element 132 in the same 1 1 different power level settings respectively, according to example embodiments.

[0056] Subplots 911 , 931 ; 912, 932; 913, 933; 914, 934; 915, 935; 916, 936; 917, 937; 918, 938; 919, 939; 920, 940; and 921 , 941 respectively show how 0%, 12.5%, 20%, 25%, 33%, 37.5%, 45%, 50%, 62.5%, 70% and 90% of the total possible power rating can be achieved at the respective 11 power level settings. For example, if both heat generating elements have a maximal power of 1000 Watt, W, the total maximal power level of the hair styling device is 2000 W. The respective power levels of the 11 power level settings would then be 0 W, 250 W, 400 W, 500 W, 666 W, 750 W, 900 W, 1000 W, 1250 W, 1400 W and 1800 W. It is noted that the power level settings could also be chosen as uniformly distributed in a chosen interval, e.g. from 0% to 90%.

[0057] At increasing power level settings, a ratio of the pulse width over the inter-pulse distance of the driving signal 251 is incremented. As the power level is increased from lowest to highest setting, only the first heat generating element is activated in the lower power level settings in subplots 911 -918, 931-938. Over the subsequent power level settings of subplots 919-921 , 939-941 , the second heat generating element is also incrementally powered. Subplots 911 -921 , 931 -941 show the powering voltages 951 -961 , 971 -981 provided to each of the heat generating elements 131 , 132 respectively after applying the driving signals. The driving signals themselves are not shown. It is noted that the driving signals can be generated as on-off signals, for example similar to the example embodiments shown in Figures 3, 4, 5, 7 and 8. In the example embodiment of Figure 10, the driving signals are constructed using units of half the period length 90.

[0058] Subplots 911 , 931 show a first setting, wherein both heat generating elements are off, thereby achieving a power of 0 W.

[0059] Subplots 912 illustrates a second power level setting wherein the first heat generating element 131 is powered on 25%, i.e. 250 W. Subplot 932 shows the powering of the second heat generating element 132 in the second setting as off, i.e. powered on 0 W. Together, the heating elements 131 , 132 achieve a 12.5% power level setting, i.e. 250 W I 2000 W. To obtain this, the driving signal 251 has a pulse width of half the period 90 and an inter-pulse distance of 3 times half the period 90. This results in the powering voltage waveform 952. Since the second heat generating element is off, the corresponding waveform 972 is a flat line at 0 V. To obtain signal 952, the corresponding driving signal 251 has pulses characterised by a pulse width equal to one time half the period length and has a time between pulses equal to three times half the period length.

[0060] Alternatively, both heat generating elements could be activated at the same power level, i.e. in this case 12.5%, in other words allowing half a period pulse through over four period lengths 90. This could be done in a time-interleaved manner to avoid simultaneous currents in the heat generating elements. Alternatively, the heat generating elements could both be activated at a different power level. For example, the first heat generating element could be powered at 10%, i.e. 100 W, while the other heat generating element is powered at 15%, i.e. 150 W. These approaches can be applied to other power level settings as well.

[0061] Subplots 913, 914, 915, 916, 917, 918 respectively show a third, fourth, fifth, sixth, seventh and eighth power level setting wherein the first heat generating element 131 is powered on 40%, 50%, 66%, 75%, 90% and 100% respectively and the second heat generating element 132 is powered off. This corresponds to 400 W, 500 W, 666W, 750 W, 900 W and 1000 W for a 1000 W heat generating element 131. Corresponding subplots 933, 934, 935, 936, 937, 938 show the power of the second heat generating element 132 in those power level settings as off, i.e. powered on 0 W. Together, the heat generating elements achieve power level settings of 20%, 25%, 33%, 37.5%, 45% and 50% respectively. In the third power level setting, see subplot 913, the driving signal 251 has pulses characterised by a pulse width equal to two times half the period length and has a time between pulses equal to three times half the period length. Since the second heat generating element is off, the corresponding waveform 973 is a flat line at 0 V. In the fourth power level setting, see subplot 914, the driving signal 251 has pulses characterised by a pulse width equal to one time half the period length and has a time between pulses equal to one time half the period length. Since the second heat generating element is off, the corresponding waveform 974 is a flat line at 0 V. In the fifth power level setting, see subplot 915, the driving signal 251 has pulses characterised by a pulse width equal to two times half the period length and has a time between pulses equal to one time half the period length. Since the second heat generating element is off, the corresponding waveform 975 is a flat line at 0 V. In the sixth power level setting, see subplot 916, the driving signal 251 has pulses characterised by a pulse width equal to three times half the period length and has a time between pulses equal to one time half the period length. Since the second heat generating element is off, the corresponding waveform 976 is a flat line at 0 V. In the seventh power level setting, see subplot 917, the driving signal 251 has pulses characterised by a pulse width equal to nine times half the period length and has a time between pulses equal to one time half the period length. Since the second heat generating element is off, the corresponding waveform 977 is a flat line at 0 V. In the eighth power level setting, see subplot 918, the driving signal 251 has pulses characterised by a pulse width equal to ten times half the period length and has a time between pulses equal to zero times half the period length. In other words, the first heat generating element 131 is continuously on and the driving signal is a constant signal allowing the input power through to the heat generating element 131 . Since the second heat generating element is off, the corresponding waveform 978 is a flat line at 0 V.

[0062] Subplots 919, 920, 921 respectively show a ninth, tenth and eleventh power level setting wherein the second heat generating element 132 is powered on 25%, 40%, and 80% respectively and the first heat generating element 131 is powered on100%. This corresponds to a total power of 1250 W, 1400 W and 1800 Wfor 1000 W heat generating elements 131 , 132. Corresponding subplots 919, 920, 921 show the power of the first heat generating element 131 in those power level settings as 100%, i.e. powered on 1000 W. Together, the heat generating elements achieve power level settings of 62.5%, 70% and 90% respectively. In the ninth power level setting, see subplot 939, the driving signal 252 has pulses characterised by a pulse width equal to one time half the period length and has a time between pulses equal to three times half the period length. Since the first heat generating element is continuously on, the corresponding waveform 919 corresponds to the input power 99. In the tenth power level setting, see subplot 940, the driving signal 252 has pulses characterised by a pulse width equal to two times half the period length and has a time between pulses equal to three times half the period length. Since the first heat generating element is continuously on, the corresponding waveform 920 corresponds to the input power 99. In the eleventh power level setting, see subplot 941 , the driving signal 252 has pulses characterised by a pulse width equal to four times half the period length and has a time between pulses equal to one time half the period length. Since the first heat generating element is continuously on, the corresponding waveform 921 corresponds to the input power 99.

[0063] Figure 9 shows a cross-sectional side view of a fourth embodiment of a hair styling device, in particular of a hair dryer 1. A housing of the hair dryer, including a casing of the main body 2 and handle 8, can for example enclose a fan 10 configured to cause air to be sucked in via the air entrance 4. The housing can further enclose a motor block 11 configured to cause the fan to rotate. The housing, e.g. main body 2, can include a narrowing 12, for example a substantially conical narrowing, towards an air exit 6. The housing, in particular said narrowing portion 12, can enclose one or more heating elements 13 configured to heat air such that the air exiting the main body 2 has a desired temperature which is higher than an air temperature at the air entrance 4. The device 1 may include an additional motor control element 102 configured to control operation of the motor, which motor control element may be positioned adjacent to said motor block 11 in the main body 2 of the hair styling device 1 . In the embodiment shown in Figure 9, the power electronics circuitry 300 is placed between the motor 11 and the at least one heat generating element 13, obtaining a cooling effect on the power electronics circuitry 300. Advantageously, this additionally allows pre-heating ofthe air before it reaches the heat generating element 13. In this example, the temperature sensor 210 is mounted on the at least one heat generating element 13.

[0064] Although the present invention has been illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied with various changes and modifications without departing from the scope thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. In other words, it is contemplated to cover any and all modifications, variations or equivalents that fall within the scope of the basic underlying principles and whose essential attributes are claimed in this patent application. It will furthermore be understood by the reader of this patent application that the words “comprising” or “comprise” do not exclude other elements or steps, that the words “a” or “an” do not exclude a plurality, and that a single element, such as a computer system, a processor, or another integrated unit may fulfil the functions of several means recited in the claims. Any reference signs in the claims shall not be construed as limiting the respective claims concerned. The terms “first”, “second”, third”, “a”, “b”, “c”, and the like, when used in the description or in the claims are introduced to distinguish between similar elements or steps and are not necessarily describing a sequential or chronological order. Similarly, the terms “top”, “bottom”, “over”, “under”, and the like are introduced for descriptive purposes and not necessarily to denote relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and embodiments of the invention are capable of operating according to the present invention in other sequences, or in orientations different from the one(s) described or illustrated above.

Claims

CLAIMS1 . A hair styling device (1 ) comprising:- at least one heat generating element (13);- a power supply input (9) configured for receiving input power (99) for powering the at least one heat generating element (13);- a power electronics circuitry (300) configured to power the at least one heat generating element (13) with a configurable heating power (350) by gating the input power (99) based on at least one driving signal (250); and- a controller (200) configured to generate the at least one driving signal (250) with a duty cycle configured according to the configurable heating power (350).

2. The hair styling device according to claim 1 , wherein the power supply input (9) is further configured for receiving alternating current, AC, input power (99), and wherein the controller (200) is further configured to generate the at least one driving signal (250) based on a periodicity of the AC input power (99) characterised by a period length (90).

3. The hair styling device according to claim 2, further comprising a zero-crossing detector circuitry for detecting zero-crossings (500) of the AC input power (99), wherein pulses (50) of the at least one driving signal (250) are aligned with the zero-crossings (500) of the AC input power (99).

4. The hair styling device according to claim 2 or 3, wherein the at least one driving signal (250) has pulses (50) characterised by a pulse width (400) equal to K times the period length (90), with K a natural number larger than zero.

5. The hair styling device according to claim 2 or 3, wherein the at least one driving signal (250) has pulses (50) characterised by a pulse width (400) equal to half the period length (90).

6. The hair styling device according to any one of the preceding claims, wherein the at least one heat generating element (13) is a plurality of N heat generating elements (131 , 132), wherein the at least one driving signal (250) is a plurality of L driving signals (251 , 252) each having a respective configurable duty cycle, and wherein the N heat generating elements (131 , 132) are powered based on the respective L driving signals (251 , 252), with N a natural number larger than one and L a natural number larger than zero.

7. The hair styling device according to any one of the preceding claims, wherein the power electronics circuitry (300) comprises at least one triode for alternating current (TRIAC) (301 ) gated by the at least one driving signal (250) for powering the at least one heat generating element (13) by gating the input power.

8. The hair styling device according to claim 6 or 7, wherein the at least one driving signal (250) is a plurality of L different driving signals (251 , 252).

9. The hair styling device according to claim 4 and claim 8, wherein the L different driving signals (251 , 252) have different pulse widths (401 , 402).

10. The hair styling device according to claim 8 or 9, wherein respective pulses (55, 56) of the L different driving signals (255, 256) are time-interleaved.

11. The hair styling device according to any one of the preceding claims, further comprising a main body (2) having a back end (3) and a front end (5), the front end including an air exit (6), wherein the main body (2) is configured to guide an airflow (600) from an air entrance (4) to the air exit (6), and wherein the power electronics circuitry (300) is placed in the airflow (600).

12. The hair styling device according to claim 11 , further comprising a motor (11 ) configured to generate the airflow (600), wherein the power electronics circuitry (300) is placed between the motor (11 ) and the at least one heat generating element (13).

13. Hair styling device according to any one of the preceding claims, further comprising a temperature sensor (210) for measuring a temperature in the hair styling device (1 ), wherein the controller (200) is further configured to adapt theconfigurable heating power based on a difference between the measured temperature and a predetermined temperature.

14. The hair styling device according to claim 13, wherein the temperature sensor (210) is mounted on the at least one heat generating element (13).

15. Method for controlling at least one heat generating element (13) in a hair styling device (1 ), the method comprising the steps of:- obtaining, by a controller (200), input power (99) for powering the at least one heat generating element (13);- generating, by the controller (200), at least one driving signal (250) with a duty cycle configured according to a configurable heating power (350);- gating, by a power electronics circuitry (300), the input power (99) based on the at least one driving signal (250) resulting in a gated power (350); - powering, by the power electronics circuitry (300), the at least one heat generating element (13) by the gated power (350).

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