Safety circuitry

Abstract

A safety circuit for a low heat capacity hair styling appliance is described. Safety circuitry may rely on intentionally designed weak links or temperature sensors, as well as electronic circuitry that may remove power from heater electrodes, as well as dual microprocessor designs.

Description

Technical Field

[0001] This invention relates to a safety circuit system and method for hair styling appliances. It also relates to a hair styling appliance having such a safety circuit system to ensure safe operation of the appliance by a user. Background Technology

[0002] There are various devices for styling hair that use heat to change its shape. Examples include straighteners, curling irons, and hair crimpers. Hair styling devices heat the hair directly above its glass transition temperature, at which temperature the hair becomes malleable. Hair is styled at temperatures above its glass transition temperature; once cooled, the hair typically retains its shape until it becomes wet again. Hair styling tools, such as straighteners (e.g....) Figure 1a and Figure 1b As shown, hair styling devices typically include a heated surface (usually defined by a heating plate) that heats the hair in contact with the heated surface. Other styling devices, such as curling irons, provide a heated surface for bending, but the principle remains the same: the hair is heated above its glass transition temperature and styled by the user.

[0003] Existing hair styling tools typically use relatively thick heating plates or heating tubes, which provide a certain amount of heat capacity. Due to this heat capacity, the heaters require time to heat up, and once heated, they may take a considerable amount of time to cool down. This heat capacity makes it difficult to control the heating of the hair, leading to either overheating or underheating. There is a growing desire to develop hair styling tools that use heaters with lower heat capacity, allowing for faster heating and cooling. Therefore, such low-heat-capacity heaters are more sensitive and easier to control.

[0004] However, the inventors have recognized that existing safety circuit systems and methods typically used to ensure the safe operation of hair styling appliances are not suitable for use with hair styling appliances that use such low-heat-capacity heaters. Therefore, there is a need for an improved safety circuit system and method that can ensure the safe operation of hair styling appliances using lower-heat-capacity heaters.

[0005] Existing hair styling tools typically use thermistors for temperature sensing to control the heating of the heater, or as part of safety to cut off power to the heater in case of overheating. However, especially when manufacturing thermistors for low-heat-capacity heaters, it is difficult to mass-produce and accurately calibrate such thermistors, leading to increased inefficiency and greater potential waste.

[0006] The purpose of this invention is to solve or at least partially eliminate one or more of the above-mentioned problems. Summary of the Invention

[0007] The invention is set forth in the appended independent claims. Optional features are set forth in the appended dependent claims. Any examples and embodiments not falling within the scope of the claims herein are not part of the invention and are provided for illustrative purposes only.

[0008] According to a first aspect, a hair drying and / or styling apparatus is provided, comprising: a heater for providing heat for drying and / or styling hair, the heater having a heating rate greater than 30°C / second; a power supply for providing power to the heater; and a safety circuit system for disconnecting the power supply from the heater in response to an overheat triggering event or a fault detection event; wherein the safety circuit system is configured to disconnect the power supply from the heater assembly during a period of 0.02 seconds to 2 seconds of the overheat triggering event or the fault detection event. Preferably, the safety circuit system is configured to disconnect the power supply from the heater assembly during a period of 0.02 seconds to 1 second of the overheat triggering event or the fault detection event, more preferably during a period of 0.025 seconds to 1 second, and even more preferably during a period of 0.05 seconds to 0.6 seconds. This period typically depends on the heating rate and the temperature difference between the trigger temperature and the maximum permissible temperature, as well as any additional waiting time associated with the activation trigger.

[0009] In some embodiments, the heater may include independently operable heater regions, and preferably, each heater region may include at least one independently operable heater electrode. The heater may be a heater assembly (and these terms are used interchangeably).

[0010] The safety circuit system can be configured to de-energize the heater based on the detection of the overheat trigger event or the fault detection event in any one (or more) of the heater areas, preferably to disconnect power to all heater electrodes based on the detection of the overheat trigger event or the fault detection event in any one (or more) of the heater areas.

[0011] In some implementations, the safety circuitry may include an array of temperature sensors independent of the temperature sensors used in the heater control system, and means for detecting whether any one (or more) of the temperature sensors indicates an overheating trigger event.

[0012] Preferably, at least one of the temperature sensor arrays is configured to be thermally connected to each heater region of the heater assembly; alternatively, at least one of the temperature sensor arrays is configured to be thermally connected to each heater electrode of the heater assembly.

[0013] In some implementations, the safety circuit system may include at least one weak link configured to melt at a (predetermined) temperature indicating an overheating trigger event, thereby disconnecting the circuit.

[0014] In some embodiments, at least one weak link may be configured to be thermally connected to at least one adjacent heater region of the heater assembly, such that the weak link is configured to melt when one or more corresponding heater regions exceed the predetermined temperature. Alternatively, at least one weak link may be configured to be thermally connected to each heater electrode of the heater assembly, such that the weak link is configured to melt when the corresponding heater electrode exceeds the predetermined temperature.

[0015] The safety circuit system can be configured to disconnect power only to the corresponding heater region and / or heater electrode(s) in response to the melting of at least one weak link.

[0016] Preferably, the at least one weak link is formed of solder, which is configured to melt between 0.02 seconds and 2 seconds of the overheat triggering event, more preferably between 0.025 seconds and 1 second, and even more preferably between 0.05 seconds and 0.6 seconds.

[0017] Preferably, the mass of the weak link is less than or equal to 1 gram. This mass can preferably be greater than or equal to 0.005 milligrams, more preferably between 0.5 milligrams and 0.1 grams (inclusive). For example, the weak link may include solder, and the mass of the solder is preferably less than or equal to 1 gram. The mass of the solder can preferably be greater than or equal to 0.005 milligrams, more preferably between 0.5 milligrams and 0.1 grams (inclusive).

[0018] In some embodiments, at least one weak link comprises a first solder material having a first melting temperature and a second solder material having a second melting temperature, preferably wherein the second melting temperature is lower than the first melting temperature. Preferably, the second solder material constitutes a connection between the first solder material and an electrical conductor of the circuit. This connection is preferably a physical (e.g., bonding) and electrical connection. The first solder material may be solder wire and / or solder strip and / or solder preform. The second solder material may be solder paste. The second solder material may be configured to form a connection (e.g., a pad). These connections may preferably have a triangular shape (points pointing towards each other). The electrical conductor is preferably a conductive trace, which may, for example, be disposed on a substrate. The substrate may be a dielectric, such as a dielectric heater plate. In other embodiments, the second melting temperature may be higher than the first melting temperature, and preferably, the second solder material constitutes a connection between the first solder material and an electrical conductor of the circuit. As an example, the second solder material may be a conductive adhesive such as epoxy resin. The at least one weak link can be deposited by heating to a temperature between the first melting temperature and the second melting temperature. At least one link can be deposited by the method described above.

[0019] Preferably, the combined mass of the first welding material and the second welding material is less than or equal to 1 gram. This combined mass is preferably greater than or equal to 0.005 milligrams, more preferably between 0.5 milligrams and 0.1 grams (inclusive).

[0020] In some implementations, the substrate on which the weak link is disposed may have a solder resist coating to facilitate the removal of molten solder and ensure that the electrical connection is broken.

[0021] The hair drying and / or styling apparatus may also include a microfluidic structure adjacent to the at least one weak link for guiding out molten material and thereby disconnecting the electrical connection.

[0022] At least one weak link can be elastically biased so that the electrical connection breaks upon melting.

[0023] At least one weak link can be deposited using a printing technique configured to achieve the small thickness required for the weak link. Preferably, this thickness can be 0.11 mm.

[0024] In some embodiments, the at least one weak link may be connected to a switch, preferably wherein the switch is configured to de-energize the heater assembly upon melting of the at least one weak link.

[0025] In some embodiments, the safety circuit system may include an array of weak links connected in series with a switch. Preferably, the switch is configured to de-energize the heater assembly upon the melting of at least one weak link in the array of weak links.

[0026] In some implementations, the at least one weak link is coupled to a switch, whereby, in the event of melting of one or more of the at least one weak link, the switch is configured to change state and prevent power from being supplied to at least one heater electrode of the heater.

[0027] The heater includes a plurality of heater electrodes, and a change in the state of the switch can prevent power from being supplied to one or more or each of the heater electrodes. Typically, the at least one link is coupled between the control gate of the switch and a reference potential (e.g., ground), such that melting of the at least one link decouples the control gate of the switch from the reference potential, thereby changing the state of the switch.

[0028] The switch can be a first switch, and a second switch can be configured to be coupled between the control gate of the first switch and the reference potential. In this case, the controller can be configured to operate the second switch to simulate the melting of the at least one link, thereby testing the operation of the first switch.

[0029] In some embodiments, the safety circuitry includes an array of nonlinear thermistors in thermal contact with the heater assembly and independent of a temperature sensor for controlling the heater, and means for detecting the voltage across the array of nonlinear thermistors. The safety circuitry is configured to cut off power to the heater assembly based on whether the voltage across the array of nonlinear thermistors exceeds or falls below a threshold indicating an overheating trigger event. (In the case of PTC or NTC thermistors, this preferably depends on whether the voltage exceeds or falls below the threshold indicating an overheating trigger event.)

[0030] At least one of the nonlinear thermistors in the array may be configured to be in thermal contact with at least one adjacent heater region of the heater assembly to monitor the temperature of the one or more heater regions. Preferably, at least one of the nonlinear thermistors in the array is configured to be in thermal contact with at least one adjacent heater electrode of the heater assembly to monitor the temperature of the heater electrode.

[0031] Preferably, the nonlinear thermistor array is connected in series. This array can be arranged in parallel, but a series arrangement typically achieves higher sensitivity.

[0032] In some embodiments, the safety circuit system includes a parallel array of temperature sensors and means for detecting whether the voltage of any one (or more) of the parallel array of temperature sensors exceeds or falls below a threshold indicating an overheating trigger event, wherein the safety circuit system is configured to cut off the power supply to the heater assembly based on detecting that the voltage of any one (or more) of the parallel array of temperature sensors exceeds or falls below the threshold indicating an overheating trigger event.

[0033] The safety circuit system may include a diode array and means for detecting the voltage output from the diode array, wherein each diode in the diode array is connected across a temperature sensor in a parallel array of temperature sensors, and wherein the safety circuit system is configured to cut off the power supply to the heater assembly based on whether the voltage output from the diode array exceeds or falls below a threshold indicating an overheating trigger event.

[0034] In some embodiments, the safety circuitry may include a multiplexer connected across the parallel array of the temperature sensors for sampling voltage, wherein the safety circuitry is configured to cut off power to the heater assembly based on the sampled voltage of any one (or more) of the parallel array of temperature sensors exceeding or falling below a threshold indicating an overheating trigger event.

[0035] In some implementations, the safety circuitry may include a first microprocessor and a second microprocessor, both configured to run software that measures the temperature of the heater assembly.

[0036] Preferably, the safety circuit system includes means for comparing outputs from the first microprocessor and the second microprocessor to detect fault detection events.

[0037] The first microprocessor and the second microprocessor can be configured to run the same software that measures the temperature of the heater assembly.

[0038] The safety circuit system may include a first connection and disconnect device connected in series with the second connection and disconnect device, wherein the first microprocessor controls the first connection and disconnect device and the second microprocessor controls the second connection and disconnect device, such that the outputs of the first microprocessor and the second microprocessor must be consistent to supply power to the heater assembly.

[0039] Preferably, the safety circuit system includes a first array of connection and disconnection devices and a second array of connection and disconnection devices, wherein a first microprocessor controls each of the first array of connection and disconnection devices, wherein a second microprocessor controls each of the second array of connection and disconnection devices, and wherein the heater includes an array of heater electrodes, each heater electrode being connected to a connection and disconnection device in the first array of connection and disconnection devices, the connection and disconnection devices in the first array of connection and disconnection devices being connected in series with the connection and disconnection devices in the second array of connection and disconnection devices, such that the outputs of the first microprocessor and the second microprocessor must be consistent for each heater electrode to ensure that the heater electrode is electrically connected to the power supply.

[0040] In some embodiments, the safety circuitry may include means for comparing the outputs of the first microprocessor and the second microprocessor for each heater electrode of the heater, wherein if the first microprocessor and the second microprocessor are inconsistent for any one (or more) of the heater electrodes, the connection and disconnection means are configured to disconnect the power supply from the heater assembly.

[0041] The first microprocessor and the second microprocessor can be configured to be fed into an XOR gate such that if the outputs of the first microprocessor and the second microprocessor are consistent (and / or, for example, identical), the XOR gate outputs logic low (0).

[0042] In some embodiments, the safety circuit system includes a series of XOR gates, each corresponding to a heater electrode of the heater assembly, wherein the first microprocessor and the second microprocessor are configured to be fed into each of the series of XOR gates with respect to the respective heater electrode.

[0043] The outputs of a series of XOR gates can be output to one or more OR gates such that if the outputs of the first microprocessor and the second microprocessor are inconsistent for any one (or more) of the heater electrodes, the safety circuit outputs logic high (1).

[0044] The outputs of a series of XOR gates can be output to one or more OR gates such that if the outputs of the first microprocessor and the second microprocessor are consistent for the heater electrode, the safety circuit outputs logic low (0).

[0045] The outputs of a series of XOR gates can be output to one or more OR gates such that if the outputs of the first microprocessor and the second microprocessor are inconsistent (e.g., not the same) for any one (or more) heater electrodes, the safety circuit outputs logic low (0).

[0046] In some implementations, the first microprocessor runs control software, and the second microprocessor runs security software.

[0047] The safety circuit system may preferably include means for sending temperature measurements to a first microprocessor and a second microprocessor.

[0048] The first microprocessor can be configured to control the heater based on temperature measurements.

[0049] The safety circuit system preferably includes a main connection and disconnection device for disconnecting power to the heater assembly, wherein the second microprocessor controls the main connection and disconnection device based on the temperature measurement.

[0050] In some embodiments, the heating assembly may include at least one thermistor, and the means for transmitting temperature measurements may include means for measuring resistance.

[0051] The heater assembly can be connected to the first microprocessor via a first connection and disconnection device controlled by the first microprocessor, and the heater can be connected to the second microprocessor via a second connection and disconnection device controlled by the second microprocessor.

[0052] In some embodiments, each heater electrode of the heater is connected to the first microprocessor via a first connection and disconnection device controlled by the first microprocessor, and the heater assembly is connected to the second microprocessor via a second connection and disconnection device controlled by the second microprocessor.

[0053] In some preferred embodiments, a first processor is configured to control the first connection and disconnection device to individually supply power to each heater electrode in order to determine the temperature measurement of that heater electrode, and / or a second processor is configured to control the second connection and disconnection device to individually supply power to each heater electrode in order to determine the temperature measurement of that heater electrode.

[0054] In some preferred embodiments, a main connection and disconnection device may be provided for disconnecting power to the heater assembly based on an overheat triggering event and / or a fault detection event.

[0055] The connection and disconnection device may include a switch, preferably a MOSFET switch.

[0056] The hair drying and / or styling apparatus may also preferably include a latching circuit system configured to introduce a delay or a semi-permanent disconnection of the power supply from the heater after an overheating trigger event or a fault detection event has occurred.

[0057] In some preferred embodiments, the safety circuitry may include a comparator for comparing a voltage with a threshold indicating an overheating trigger event or a fault detection event.

[0058] The safety circuit system may include a switch for controlling the power supply to the heater assembly, preferably a MOSFET switch, and / or preferably wherein the output of the comparator controls the switch. This switch may be the same as the main connection and disconnection device.

[0059] A computer program product for implementing software (e.g., security software and / or control software) (such as software running on a first processor and / or a second processor) may also be provided. Additionally, a (tangible) non-transitory computer-readable product comprising instructions that, when executed by a processor, implement software (e.g., security software and / or control software) may be provided. Furthermore, a signal for implementing software (e.g., security software and / or control software) may be provided.

[0060] According to another aspect of the invention, a safety circuit system for a hair styling tool is provided, comprising a heater assembly having a heating rate greater than 30°C / second, wherein the safety circuit system is configured to disconnect (or cut off) the power supply to the heater assembly during a period of 0.02 seconds to 2 seconds after an overheating trigger event or a fault detection event.

[0061] The safety circuit system may also preferably include any of the safety circuit system features described above.

[0062] According to another aspect of the present invention, a method for fabricating a weak link for a security circuit system is provided, comprising: applying a first soldering material to form a first connector at an end of a first conductor and a second connector at an end of a second conductor, wherein the first soldering material has a first melting temperature; applying a second soldering material such that it connects the first connector and the second connector, wherein the second soldering material has a second melting temperature higher than the first melting temperature; and heating to a temperature between the first melting temperature and the second melting temperature (preferably, thereby connecting the second soldering material to the first conductor and the second conductor via the first connector and the second connector, respectively).

[0063] The method may also preferably include a cooling step. The first welding material may be a welding rod and / or welding strip and / or a solder preform and / or a solid block.

[0064] The method may further include depositing solder resist material in the region between the ends of the first conductor and the ends of the second conductor. The method may also include depositing solder resist material in the region of the second solder material. The method may further include depositing solder resist material on a substrate on which the first and second solder materials have been applied.

[0065] The first conductor and the second conductor can be conductor traces, preferably conductor traces on a dielectric layer.

[0066] Weak links can be configured to be adjacent to heaters (e.g., heater electrodes).

[0067] The method may also include connecting the weak link to a switch, preferably a control switch.

[0068] In a preferred embodiment of the method, the steps may be performed on a heater for hair drying and / or styling appliances, and preferably on a medium layer of the heater for hair drying and / or styling appliances.

[0069] The invention extends to methods and / or apparatus that are substantially as described herein with reference to the accompanying drawings.

[0070] Any device feature described herein may also be provided as a method feature, and vice versa.

[0071] According to another aspect, a hair drying and / or styling apparatus is provided, comprising a calibrated thermistor, wherein the calibrated thermistor includes: a first thermistor main line having a first impedance; a second thermistor main line having a second impedance; and a plurality of thermistor calibration lines, each thermistor calibration line having its own impedance, and wherein the plurality of thermistor calibration lines are electrically connected in parallel with each other and electrically connected in series with the first and second thermistor main lines, wherein at least one of the plurality of thermistor calibration lines is disconnected to provide the calibrated impedance of the calibrated thermistor. Advantageously, this provides a calibrated thermistor for a hair drying and / or styling apparatus.

[0072] In one example, a hair drying and / or styling apparatus including a calibrated thermistor is provided, wherein the calibrated thermistor includes: a first thermistor main line having a first impedance; a second thermistor main line having a second impedance; and a plurality of thermistor calibration lines, each thermistor calibration line having a first end, a second end, and its own impedance, wherein the first ends of the plurality of thermistor calibration lines are electrically connected to each other and to the first thermistor main line, and the second ends of the plurality of thermistor calibration lines are electrically connected to each other and to the second thermistor main line, wherein at least one of the plurality of thermistor calibration lines is disconnected to provide the calibrated impedance of the calibrated thermistor.

[0073] Optionally, at least one of the first thermistor main line, the second thermistor main line, and a plurality of thermistor calibration lines is printed on the surface of the hair drying and / or styling device or other substrate. Advantageously, this means that no additional substrate is required to manufacture the thermistor, and the thermistor is manufactured by printing rather than using conventional surface mount components.

[0074] Optionally, the first thermistor main line and the second thermistor main line have the same impedance.

[0075] Optionally, at least two of the multiple thermistor calibration lines have the same impedance when not disconnected. Advantageously, this means that in the presence of multiple calibration lines with the same impedance and when one calibration line needs to be disconnected, any one of them can be disconnected instead of selecting a particular line.

[0076] Optionally, at least two of the multiple thermistor calibration lines have different impedances when not disconnected. Advantageously, this means that multiple calibration lines can exist, which can provide different amounts of variation in the total thermistor impedance, thus offering greater choice during the calibration process.

[0077] Optionally, the impedance of at least one of the first and second thermistor main lines is lower than the impedance of at least one of the plurality of thermistor calibration lines. Advantageously, this means that the calibration lines offer a greater number of possible calibrations relative to the total impedance of the thermistors.

[0078] Optionally, the impedance of at least one of the first and second thermistor main lines is higher than the impedance of at least one of the plurality of thermistor calibration lines. Advantageously, this means that the calibration lines provide fine-tuning relative to the total impedance of the thermistors.

[0079] Optionally, multiple thermistor calibration leads are individually disconnectable. Advantageously, this means that each calibration lead can be disconnected, and the total impedance can be checked each time, rather than having to disconnect multiple leads at once and causing the calibration process to overshoot.

[0080] Optionally, the calibrated thermistor forms part of the thermal safety circuit for the heater of the hair styling device, or part of a sensor circuit for sensing the temperature of the heater of the hair styling device.

[0081] In another aspect, a method is provided for manufacturing a hair drying and / or styling apparatus having a calibrated thermistor, the method comprising: setting a first thermistor main line having a first impedance; setting a second thermistor main line having a second impedance; setting a plurality of thermistor calibration lines, each thermistor calibration line having its own impedance, wherein the plurality of thermistor calibration lines are electrically connected in parallel with each other and electrically connected in series with the first thermistor main line and the second thermistor line; calibrating the impedance of the thermistor to be within a desired tolerance range of a desired impedance; and incorporating the calibrated thermistor into the hair drying and / or styling apparatus.

[0082] Optionally, calibrating the impedance of the thermistor to be within the desired tolerance range of the desired impedance includes: measuring the impedance of the thermistor at a set temperature and comparing the measured impedance with the desired impedance.

[0083] Optionally, calibrating the thermistor further includes: selecting at least one of a plurality of thermistor calibration lines based on a comparison of the measured impedance with the desired impedance; and disconnecting the selected at least one thermistor calibration line.

[0084] Optionally, disconnecting the selected at least one thermistor calibration line includes using a laser to disconnect at least one thermistor calibration line. Advantageously, this means that physical contact with the thermistor or device is not required to calibrate the thermistor.

[0085] Optionally, calibrating the thermistor's impedance to be within the desired tolerance range of the desired impedance further includes: determining, based on a comparison of the measured impedance with the desired impedance, to provide at least one additional thermistor calibration line; and printing at least one additional thermistor calibration line in series with the first and second thermistor main lines. Advantageously, this means that the thermistor's impedance can also be reduced during the calibration process.

[0086] Any feature in one aspect of the invention may be applied to other aspects of the invention in any suitable combination. Specifically, a method aspect may be applied to an apparatus aspect, and vice versa. Furthermore, any, some, and / or all features in one aspect may be applied to any, some, and / or all features in any other aspect in any suitable combination.

[0087] It should also be understood that specific combinations of the various features described and defined in any aspect of the invention may be implemented independently and / or provided and / or used. Attached Figure Description

[0088] One or more aspects will now be described by way of example only, and with reference to the accompanying drawings which have the same reference numerals: Figure 1a A hair styler was shown; Figure 1b It shows users using hair stylers on their hair; Figure 2a An exploded view of a low heat capacity heater is shown; Figure 2b It shows Figure 2a Transparent assembly perspective view of the low heat capacity heater shown; Figure 2c It shows Figure 2a An opaque assembly perspective view of a low heat capacity heater shown. Figure 2d A weak link that can be used in thermal safety circuits is shown; Figure 3a A first arrangement of the heater area on the heating surface of the hair styling heater is schematically shown; Figure 3b A second arrangement of heater areas disposed on the heating surface of a hair styling heater is schematically shown; Figure 4 It is a temperature-time curve of the heating response of a low heat capacity heater; Figure 5 This is a schematic circuit diagram illustrating the operation of a thermal safety circuit used to isolate the heating circuitry of a hair styler; Figure 6 This illustrates one form of a thermal safety circuit system; Figure 7 An alternative form of thermal safety circuit is shown; Figure 8 Another example of a thermal safety circuit is shown; Figure 9 Another example of a thermal safety circuit is shown; Figure 10Examples of printed and laser-calibrated ladder thermistors are shown; Figure 11 This is a partially exploded cross-sectional perspective view of another heater assembly; Figure 12a This is an exploded view of the flexible heater, adhesive layer, and heater support, viewed from above. Figure 12b It is observed from below. Figure 12a An exploded view of the flexible heater, adhesive layer, and heater support shown. Figure 13 The composition is shown Figure 11 The main heating electrode layer is shown as a portion of the heater. Figure 14 The composition is shown Figure 11 The heater shown is a portion of the heat diffusion filament layer; Figure 15 shows more details Figure 14 The fuse circuit system shown; Figure 16a yes Figure 11 The diagram shows a cross-sectional view of a portion of the heater assembly, revealing an intact fuse. Figure 16b yes Figure 11 The diagram shows a cross-sectional view of a portion of the heater assembly, illustrating when the fuse melts due to overheating; and Figure 17 This is a simplified schematic diagram of a drive and control circuit system that can be used to control... Figure 11 The heater shown is used for heating. Detailed Implementation

[0089] The embodiments described below represent the best way known to the inventors to put the invention into practice. However, they are not the only way to achieve this.

[0090] Overview of hair stylers

[0091] Figure 1a A hair styler 1 is shown. The hair styler 1 includes a first movable arm 4a and a second movable arm 4b, which are coupled to a shoulder 2 at their proximal ends. The first arm 4a supports a first heater 6a at its distal end, and the second arm 4b supports a second heater 6b at its distal end. The first heater 6a and the second heater 6b are opposite each other and are brought together when the first arm 4a and the second arm 4b are moved from an open configuration to a closed configuration. Hair can be inserted between and in contact with the heating surfaces of the heaters 6a, 6b, in which the heaters 6a, 6b apply conductive heat to the hair for styling.

[0092] Heaters 6a and 6b are low heat capacity heaters, and therefore can heat and cool rapidly. Figures 2a to 2c An exemplary embodiment of such heaters 6a, 6b is shown, which includes a stack of thin layers. See specifically for... Figure 2a Heaters 6a and 6b include an upper dielectric (electrically insulating) layer 62, an electrode layer 63 having a plurality of heater electrodes 64, and a lower dielectric layer 66 electrically insulating the heater electrodes 64 from other components mounted behind heaters 6a and 6b. These three layers 62, 63, and 66 are bonded together and define a heater with a very low heat capacity. The upper surface of layer 62 provides a hair contact surface, but a non-stick coating can be applied to the upper surface of layer 62 to allow user hair to pass through the heating surface. The hair contact surface of the heater is a single smooth surface over which hair can pass. The adhesive layers 62, 63, and 66 define a flexible heater, and in the illustrated embodiment, the heater rigidity is provided by mounting heater layers 62, 63, and 66 into a rigid support 68 constituting the base. If a flexible heater is required, the rigid support 68 is not necessary. Typically, under low-voltage operation (less than about 40 volts), the total thickness across multiple adhesive layers is between 30 micrometers and 2 mm (preferably between 75 μm and 300 μm), and under AC operation, the total thickness is between 0.8 mm and 2.0 mm.

[0093] In the illustrated embodiment, there are ten heater electrodes 64, each serpentinely traversing the width of heater 6, folding twice such that each heater electrode spans the width three times. The ends of each heater electrode 64 are electrically connected via a substrate 66 to an electrical connection within a rigid support 68, which is connected to an electrical connector 70. A drive circuitry system (not shown) mounted within one of the arms 4 is connected to the heater electrodes 64 via the electrical connector 70 and applies current to each heater electrode 64 to control the heat generated by each heater electrode 64. The electrical connector 70 extends from the surface of the rigid support 68 away from the surface layer 62 (in... Figures 2a to 2c It is shown as extending directly away from the upper layer 62, but it can also be set to extend in the vertical direction.

[0094] Therefore, each heater electrode 64 in this series generates a separate heater region that spans the width of the heater 6 (referred to as the x-direction), and the heater electrodes 64 are arranged one after another along the length of the heater 6 (y-direction). Figure 3a and Figure 3b Schematic diagrams showing different arrangements of such heating zones are provided. Figure 3a It shows the relationship with Figures 2a to 2c The arrangement corresponds to the arrangement of the heating area 642, which is arranged only along the y-direction. Figure 3bAn alternative arrangement is shown, in which the heating area 644 is arranged in both the x and y directions. This can be achieved by arranging two sets of [likely referring to a specific arrangement] side-by-side in the width direction (x direction). Figure 2a The heater electrodes 64 shown are arranged to provide the heating region 644 in this manner. The heater 6 can be divided into any number of regions in this way, and can include any number of regions along the x and y directions. Specifically, although Figure 3b Two regions along the x-direction are shown, but more regions along the x-direction could also be provided. Regions 642 and 644 of heaters 6a and 6b can operate (heat) independently, which can help reduce cold spots when using heaters 6 with very low heat capacity (such as those shown in Figure 2).

[0095] Because heater 6 has a very low heat capacity, it heats up and cools down much faster than existing heaters that use relatively thicker heater plates. While a typical conventional hair styler from the environment might take 30 seconds to reach its operating temperature of approximately 200°C, a low-quality heater at maximum power might exceed the same temperature in one second (or less). However, the exact operating temperature and heating time are determined by requirements, heat capacity, and maximum power. For illustration, a heater that can reach 200°C at maximum power is described. -1 Heating rate.

[0096] To ensure user safety, the maximum temperature that heater 6 can reach must be limited in the event of electronic device or firmware failure. For illustrative purposes, Figure 4 This is a temperature-time curve of heater 6 operating at maximum power. In this example, the operating temperature T... operating The maximum permissible temperature T for heater 6 to operate safely is set to 230°C. max Defined as 300℃. Trigger temperature T trigger A temperature is defined as the temperature above which the safety fuse mechanism is triggered to cut off power to heater 6. In this example, T trigger It is set to 240℃. If T trigger If set too low, there is a risk that the safety fuse may be triggered by small fluctuations near the operating temperature. However, if T... trigger If it's too high, the fuse may not react quickly enough to prevent the temperature from rising above T. max This could be a particular problem for heater 6, which has a very low heat capacity, as shown in Figure 2. Figure 4 The example shown is if the heater has a temperature of 200 °C. -1 At its maximum heating rate, a 0.3-second response time of the thermal safety fuse is required to prevent the temperature from rising to T. max above.

[0097] The use of thermal safety fuses in hair styling tools is known to prevent overheating and ensure safety. However, the fastest response rate of commercially available thermal fuses is typically only 40°C. -1 Therefore, if such a hot fuse is used with a low-heat-capacity heater, the high heating rate may cause heaters 6a and 6b to reach extremely high temperatures before the hot fuse can cause power to be cut off from heater electrodes 64. This could pose a safety risk to the user, and the present invention seeks to provide a thermal safety circuit breaker system that can react quickly enough to a fault to prevent such unsafe operation when using a very low-heat-capacity heater 6.

[0098] The mechanisms of this invention provide independent circuit breaking circuits. In addition to the functions of the main controller CPU, these mechanisms are typically provided to routinely monitor for faults during normal operation.

[0099] As will be described in more detail below, the increased breaking speed of the thermal safety circuit-breaking system of the present invention can be achieved by setting intentionally designed weak components, by electronic devices, or by a microprocessor-based security strategy. The thermal safety circuit-breaking of the present invention can disconnect power to the gate of a main metal-oxide-semiconductor field-effect transistor (MOSFET), which controls the drive circuit's ability to supply power to the heater 6. Figure 5 An exemplary block diagram of the connection between thermal safety circuit 102 and heating circuit 104 (which includes a heater 6 with very low heat capacity) is shown. As shown, thermal safety circuit 102 controls the voltage applied to the gate of MOSFET switch 106, which isolates heating circuit 104 from ground, thereby preventing current from flowing through heater electrode 64 of heater 6.

[0100] Several different thermal safety circuits 102 will now be described.

[0101] Example 1 – Utilizing Intentionally Designed Weak Components

[0102] In a first embodiment, a deliberately designed weak component is provided in the thermal safety circuit. In an exemplary embodiment, the deliberately designed weak component is a solder link designed to melt at a set temperature, thereby breaking the electrical link of the thermal safety circuit. This removes voltage from the gate of MOSFET 106, which disconnects the heater 6 in the heating circuit 104 from ground, thereby preventing current from flowing through the heater electrode 64.

[0103] In some embodiments, the weak links may be located at or near the hair contact surface of the upper layer 62, but preferably at a distance from the hair surface. A suitable thermally conductive (but preferably electrically insulating) material may be located on and / or around the weak links to ensure they respond adequately to temperature increases. Preferably, these weak links are mounted close to the heater electrodes 64 such that they are subjected to as much heat flux generated by the heater electrodes 64 as possible. In one embodiment, these weak links are mounted on the back side of the dielectric layer 66 (on the surface facing the rigid support 68). A separate weak link may be provided near each heater electrode 64, designed to melt when the corresponding heater electrode 64 becomes overheated. This weak link may be designed to cut off power only to the corresponding heater electrode 64, or to cut off power to all heater electrodes 64. Each weak link may be located near multiple heater electrodes 64 and may be designed to melt when any of the adjacent heater electrodes 64 becomes overheated.

[0104] The weak link can be formed by welding material. The preferred arrangement of the weak link is in... Figure 2d shown in . Specifically, Figure 2d A portion of the back side of dielectric layer 66 is shown, on which two conductor traces 71-1 and 71-2 are mounted. The closest ends of the two conductor traces 71 are connected to corresponding pads 72-1 and 72-2 for receiving solder paste with a first melting temperature. Once solder paste is applied to the pads 72, a solid solder block 74 (e.g., wire or ribbon, sometimes referred to as a "solder preform") with a melting temperature higher than that of the solder paste 72 is placed between the two pads 72, thereby forming an electrical connection between the two conductor traces 71. The weak link is then heated in a furnace to a temperature between the melting temperature of the solder paste and the melting temperature of the solder block 74 to melt the solder paste (but not the solder block 74). The heater is then removed from the furnace, allowing the solder paste to solidify and bond the solder block 74 to the pads 72. Thus, the weak link (fusible solder link) comprises both the solder preform (wire / ribbon) and the solder paste. In an alternative arrangement, instead of using solder paste that melts to adhere to the solder block, conductive epoxy resin (which does not melt at all) can be used to adhere the solder block to the pad 72.

[0105] The surface of the dielectric layer 66 surrounding the weak link (at least in the gap between pads 72-1 and 72-2) is covered with a solder resist material 76 that repels solder. The melting temperature of the solder block 74 is selected such that, during use, if the heater 64 overheats, the solder block 74 melts within an allowable response time. The molten solder is repelled by the solder resist 76, which ensures that the solder is rapidly drawn away from the gap between the two conductor traces 71, thereby breaking the connection between the conductor traces 71. Figure 2dThe weak links shown can be located on the underside of the dielectric layer 66 adjacent to each heater 64. Each weak link can be connected back to the corresponding switch 106, or the weak links can be connected in series back to the common control switch 106. Thus, one or more control switches 106 can detect whether any weak link has melted and remove power from the heater 64 accordingly.

[0106] To ensure that the weak link disconnects the power supply within the required response time, each fusible solderable link is made of a combination of solder paste and solder wire / strip, the combined mass of which ranges from 0.005 mg to 1 gram (inclusive), more preferably from 0.5 mg to 0.1 gram (inclusive). In an alternative arrangement using epoxy resin to bond the solder blocks, the solder has a mass between 0.005 mg and 1 gram (inclusive), more preferably between 0.5 mg and 0.1 gram (inclusive).

[0107] Ensuring that the circuit reliably disconnects above a set temperature can be beneficial. In another exemplary embodiment of the above, this can be achieved by using a microfluidic structure (e.g., a channel) configured to facilitate the flow of molten solder away from the connection point, thereby reliably disconnecting the circuit. In yet another exemplary embodiment, the solder link is elastically biased (e.g., spring-loaded) to ensure that the circuit is reliably and completely disconnected when the solder melts at the set temperature.

[0108] In some implementations, weak links may include solder links with very small thicknesses. This implementation requires precise and accurate manufacturing methods. Hot air solder leveling (HASL) processes typically result in uneven solder thickness and are therefore generally unsuitable. In some exemplary embodiments of this invention, weak components such as solder links are deposited onto the PCB using printing techniques. This method is useful in achieving the desired small size thickness.

[0109] Although the MOSFET switch 106 used in this embodiment is an enhancement-mode MOSFET, a depletion-mode MOSFET switch can be used instead. In this case, a voltage divider and / or comparator can be provided between the circuit containing the weak component and the MOSFET to control the opening and closing of the MOSFET switch.

[0110] Example 2 – Utilizing a sensor with a nonlinear temperature coefficient

[0111] In a second embodiment, a thermal safety circuit is provided, which includes components that respond to temperature changes in a non-linear manner. Figure 6An exemplary circuit diagram is shown, including a thermal safety circuit 202 that controls the power supply to the heating circuit 204 via a MOSFET switch 206. The thermal safety circuit 202 includes an array of nonlinear thermistors 208, in this example four thermistors 208a to 208d connected in series. The thermistors 208 are also arranged close to the heater electrodes 64, preferably mounted on the back side of the dielectric layer 66 (on the surface facing the rigid support 68). The thermistors 208 may be arranged over the heating area defined by the heater electrodes 64. In this exemplary embodiment, only four thermistors 208 are used in the heater design shown in FIG. 2, along with ten heater electrodes 64. In other embodiments, one or more thermistors 208 may be configured adjacent to each heater electrode 64.

[0112] The nonlinear thermistors 208a to 208d can be nonlinear positive temperature coefficient (PTC) thermistors, which have a critical temperature T. c The above process results in a sharp increase in resistance. Preferably, the critical temperature T of the PTC thermistor used is... c Set to correspond to or at least be related to the aforementioned trigger temperature T trigger The DC power supply 209 (e.g., the battery of a hair styler) applies voltage to a network of series-connected thermistors 208. This network of series-connected thermistors 208, together with resistor R, defines a voltage divider circuit. Comparator 210 is connected to this voltage divider circuit and compares the voltage drop across resistor R with a reference voltage V. ref A comparison is made. When the temperature of heater 6 is low or within its normal operating temperature range (i.e., below the critical temperature T), c When the voltage drop across resistor R is greater than the reference voltage, the output of comparator 210 will be a logic high value that keeps MOSFET switch 206 on; therefore, heating circuit 204 is grounded, and heating of heater electrode 64 can continue normally. However, if the temperature of one or more heater electrodes 64 exceeds the trigger temperature, the resistance of the thermistor(s) closest to (one or more) heater electrodes 64 will increase significantly, which will increase the resistance of the thermistor network and thus decrease the voltage drop across resistor R. When the voltage drop across resistor R drops below the reference voltage V... ref When this happens, the comparator output will change from high to low, which turns off the MOSFET switch 206, thereby isolating the heating circuit 204 from ground. As a result, the current through the heater electrode 64 will stop, which will lower the temperature of the heaters 6 and prevent them from reaching the aforementioned maximum permissible temperature T. max .

[0113] like Figure 6As shown, latch circuitry 214 is positioned between comparator 210 and MOSFET 206 to keep MOSFET 206 off once comparator 210 switches it off. This ensures that comparator 210 does not re-turn on MOSFET 206 when the heater cools slightly. Specifically, latch circuitry 214 is used to introduce a delay or semi-permanent disconnect between comparator 210 and MOSFET 206. Latch circuitry 214 may include counter circuitry to define the introduced delay, or it may need to be reset by the main controller or by a power cycle event before allowing MOSFET 106 to be re-turned on.

[0114] In an alternative implementation, a negative temperature coefficient (NTC) thermistor can be used instead of a PTC thermistor, which, when its temperature rises to the critical temperature T... c At temperatures above this level, its resistance decreases sharply. Similarly, the critical temperature T... c Corresponding to or at least related to the aforementioned trigger temperature T of the heater electrode 64 trigger This is relevant. In this embodiment, when the temperature of heater 6 is low or within its normal operating temperature range (i.e., below the critical temperature T), c When the temperature of one or more heater electrodes 64 exceeds the trigger temperature, the voltage drop across resistor R will be lower than the reference voltage, and in this case, comparator 210 is configured to output a high voltage that keeps MOSFET switch 206 on; therefore, heating circuit 204 is grounded, and heating of heater electrode 64 can continue in the normal manner. This can be achieved by swapping the inputs on comparator 210, such that the reference voltage is applied to the positive input of comparator 210, and the voltage drop across resistor R is applied to the negative input of comparator. When the temperature of one or more heater electrodes 64 exceeds the trigger temperature, the resistance of one or more thermistors 208 closest to heater electrode(s) 64 will decrease significantly, which will reduce the resistance of the thermistor network, which will in turn increase the voltage drop across resistor R. When the voltage drop across resistor R rises to the reference voltage V... re When the above occurs, comparator 210 will output a low voltage, which turns off MOSFET switch 206, thereby isolating heating circuit 204 from ground. As a result, the current through heater electrode 64 will stop, which will reduce the temperature of heater 6 and prevent them from reaching the aforementioned maximum permissible temperature T. max .

[0115] Although the MOSFET switch 206 used in the example above is an enhancement-mode MOSFET, a depletion-mode MOSFET switch 206 can be used instead. In this case, the comparator 210 will be configured to output a low value when the MOSFET is on and a high value when the MOSFET is off.

[0116] In the above embodiment, thermistors 208 are connected in series with each other. In another embodiment, a network of nonlinear thermistors 208a to 208d is connected in parallel with each other. For example, if the thermistors are nonlinear negative temperature coefficient (NTC) thermistors, a decrease in the resistance of at least one thermistor will decrease the total resistance of the parallel thermistor network, thereby increasing the voltage drop across resistor R input to comparator 210. Comparator 210 then operates in the same manner as described above to control the state of MOSFET switch 206.

[0117] Preferably, a PTC thermistor and / or an NTC thermistor with high temperature sensitivity (percentage change per degree Celsius) is used, so that the thermal safety circuit 202 rises above the trigger temperature T. trigger The temperature response is excellent. This helps ensure a rapid response time to any overheating of heater 6. This high temperature sensitivity is provided by the nonlinear thermistor 208.

[0118] Example 3 – Analog OR gate for maximum area temperature sensing

[0119] In a third embodiment, a thermal safety circuit is provided, comprising an array of individual temperature sensors fed into a parallel array of diodes that act as analog OR gates, such that the thermal safety circuit isolates the heating circuit from ground if the sensed temperature from any of the individual temperature sensors exceeds a threshold.

[0120] Figure 7An exemplary embodiment is shown, in which a thermal safety circuit 302 is provided, comprising an array of temperature sensors 308a to 308d arranged in parallel. Each branch of the parallel circuit is connected to a DC power supply 309 and includes temperature sensors 308a to 308d and resistors 314a to 314d connected in series. Temperature sensors 308a to 308d are implemented as thermistors. Diodes 312a to 312d are connected to each branch of the circuit between the corresponding temperature sensors 308a to 308d and resistors 314a to 314d. The outputs of diodes 312 are connected together and fed into comparator 310. The output of comparator 310 then controls MOSFET switch 306 as previously described to control the ability to supply power to heater electrode 64 of heating circuit 304. As in embodiment 2, the output of comparator 310 is input to latching circuit system 314, which ensures that once the heater cools down slightly, MOSFET 306 cannot be turned on again, and the output of comparator 310 returns to a logic high value. In practice, all embodiments will typically include some form of latching circuitry to ensure that once the thermal safety circuitry has removed power from the heater, the device cannot start heating again (for a defined period of time or until the device is reset).

[0121] The thermistor can be a PTC thermistor or an NTC thermistor. In the case of a PTC thermistor, if any (or more) of thermistors 308a to 308d detects a temperature above the trigger temperature, its resistance will increase significantly, causing the voltage drop across the thermistor 308 to increase to the reference voltage V. ref (This can be a reference voltage different from the reference voltage used in other embodiments.) The highest voltage input to diode 312 will reach comparator 310 through diode 312, causing the comparator to change state from high to low, thus turning off MOSFET switch 306 and isolating heating circuit 304 from ground. In this way, diode 312 acts as an analog OR gate, which will output a high voltage if any input voltage to diode 312 is high. A similar arrangement can be provided for NTC type thermistors when using the depletion-type MOSFET device of Embodiment 2 as described above.

[0122] As an alternative embodiment, the diodes constituting the analog OR gate can be replaced by a scanning analog multiplexer that sequentially samples the thermistor / resistor outputs and applies them to the comparator. This embodiment offers the advantage of eliminating any voltage drop and leakage current that may be caused by the diodes.

[0123] Thermistors 308 are again arranged close to the heater electrodes 64, preferably mounted on the back side of the dielectric layer 66 (on the surface facing the rigid support 68). Thermistors 308 may be arranged over the heating area defined by the heater electrodes 64. In this exemplary embodiment, only four thermistors 308 are present in the heater design shown in FIG. 2, along with ten heater electrodes 64. In other embodiments, one or more thermistors 208 may be configured to be adjacent to each heater electrode 64 (heater area).

[0124] In another embodiment, a single thermistor can be "shared" by multiple regions, for example, if arranged in a suitable pattern such that it bridges two adjacent regions, or is placed at the corner of four adjacent regions. An array of thermistors can span multiple regions.

[0125] As an alternative to using a thermistor as the temperature sensing element, a printed thermocouple or other temperature sensing element can be used. In some implementations, a combination of different sensing elements can be used; for example, different types of temperature sensors for different areas and / or some or each of the heating areas can be combined to achieve different temperature sensing elements.

[0126] Example 4 – Dual Microprocessors

[0127] Overheating of heater electrode 64 could potentially occur due to several different faults. One potential fault leading to overheating of heater electrode 64 is that the microprocessor (used to control the heating of heater electrode 64) malfunctions and outputs incorrect control signals to control the heating of heater electrode 64. In the fourth embodiment, a safety strategy is implemented by running the same software that directly measures the heater electrode temperature on two identical microprocessors. If the two software circuits are inconsistent, the system "trips" and cuts off power to heater electrode 64.

[0128] Figure 8An exemplary implementation of this embodiment is shown in Figure 2. As shown, an array of n heater electrodes 64 is provided, four of which are shown and labeled 64a, 64b, 64c, and 64n. These heater electrodes 64 are arranged on the area to be heated by the heater 6 (as shown in Figure 2). A first microprocessor 412 and a second microprocessor 414 are also provided. One end of each heater electrode 64 is connected to a DC power supply 409, typically used to power a battery for the hair styling device, and the other end is connected to two MOSFET switches 404 and 406 connected in series (e.g., heater electrode 64a is connected to MOSFET gates 404a and 406a). The gates of the first set of MOSFETs 404 are connected to and controlled by the first microprocessor 412 (e.g., the gate of MOSFET 404a is connected to output 5 of the first microprocessor 412; MOSFET 404b is connected to output 6, etc.). The gates of the second group of MOSFETs 406 are connected to the output of the second microprocessor 414 in a similar manner (e.g., MOSFET 406a is connected to output 5 of the second microprocessor 414; MOSFET 406b is connected to output 6 of the second microprocessor 414, and so on). The source terminals of the MOSFETs 406 are connected together and grounded through a resistor R. Therefore, in operation, when current is applied to the heater electrode 64, the first microprocessor 412 must output an appropriate control signal to turn on the corresponding MOSFET switch 404, and the second microprocessor 414 must output a corresponding control signal to turn on the corresponding MOSFET switch 406, so that current can flow through the heater electrode 64, MOSFET switch 404, and MOSFET switch 406, and grounded through the resistor R. If microprocessors 412 and 414 output different control signals, causing only one of MOSFETs 404 and 406 to turn on, the corresponding heater electrode 64 will not be grounded, and therefore no current will flow through the heater electrode 64. This arrangement can serve as a fault protection operation for the circuit system in the event of a failure of one of the microprocessors.

[0129] Additionally, for a given heater electrode 64, the outputs from the first microprocessor 412 and the second microprocessor 414 are also fed to the corresponding XOR gate 408. For example, the output 5 of the first microprocessor 412 and the output 5 of the second microprocessor 414 are input to the first XOR gate 408a. For each XOR gate 408, if the software running on the first microprocessor 412 is consistent with the parallel software running on the second microprocessor 414, the inputs to the corresponding XOR gate will be the same, and in this case, the output from the XOR gate will be logic low (0). However, if the software running on the two microprocessors 412 and 414 is inconsistent, their control outputs will be inconsistent, and the corresponding XOR gate 408 will output logic high (1).

[0130] The output from XOR gate 408 passes through OR gate 410 (in Figure 8 The OR gates 410a to 410c are shown in the diagram, such that if there is any inconsistency in the control signals output from the two microprocessors 412 and 414, this will be marked as a high logic level at input 3 of each microprocessor. On the other hand, if all the corresponding control signals match each other, the output from the OR gate will be a logic low (0) level, which is fed to input 3 of each microprocessor.

[0131] If a logic high signal is received at input 3 of microprocessors 412 and 414, both microprocessors 412 and 414 can be programmed to change their output control signals, thereby turning off MOSFETs 404 and 406 to prevent any current from flowing through any heater electrode 64. Alternatively, a separate "master" MOSFET switch (not shown) controlled by one of the microprocessors can be provided between the DC power supply 409 and the heater electrode 64, such that in the event of inconsistent control signals, one of the microprocessors can turn off this master MOSFET switch, thereby removing power from all heater electrodes 64. Alternatively, for redundancy, two master MOSFET switches connected in series can be provided between the DC power supply 409 and the heater electrode 64, wherein the two master MOSFET switches are controlled by two different microprocessors. In this way, if one of the microprocessors fails, the other can still be relied upon to turn off the corresponding master MOSFET switch, which will remove power from all heater electrodes 64. This redundancy has, of course, been provided by turning off MOSFET switches 404 and 406. Figure 8 In the circuit shown, both the first microprocessor 412 and the second microprocessor 414 receive temperature sensor signals for each region of the heater 6. This is achieved using a resistor R and an operational amplifier 415. Specifically, in this embodiment, each heater electrode 64 is formed of a material whose resistance changes with the temperature of the heater electrode 64. For example, the heater electrode 64 can be formed of a PTC-type material, such that the resistance of the heater electrode 64 increases with its temperature. Of course, an NTC-type material can also be used. Figure 8As shown, each heater electrode 64 forms a voltage divider with resistor R. Therefore, the voltage at the positive terminal of amplifier 415 will depend on the temperature of the heater electrode 64. To obtain a temperature sensor signal for the desired heater electrode 64, corresponding switches 404 and 406 are turned on, and the other heater electrodes 64 are isolated from resistor R by ensuring their corresponding MOSFET switches 404 and 406 are turned off. The output signal of amplifier 415 will vary with the temperature of the desired heater electrode 64, and this signal is fed back to input 2 of each microprocessor 412 and 414. Microprocessors 412 and 414 can then cycle through each heater electrode 64 one at a time, connecting each heater electrode 64 to resistor R to obtain a temperature sensor signal for each heater electrode 64. If needed, the temperature sensor signal from amplifier 415 can be converted into an actual temperature measurement of the heater electrode 64 via an appropriate formula or lookup table. Alternatively, the control loop can directly use these temperature sensor signals in control loop calculations. This temperature sensor signal can be obtained simultaneously with or interleaved with powering the heater electrode 64 to heat the heater 6 and thus style the user's hair. Microprocessors 412 and 414 then use the temperature sensor signals or converted temperatures for the different heater electrodes 64 as part of a feedback loop to control the power supply to the heater electrodes 64, thereby maintaining a desired temperature for each heater electrode 64 (which may be the same for each heater electrode 64 or may be different for each heater electrode 64).

[0132] Example 5 – Dedicated Security Microprocessor

[0133] In the fifth embodiment, in addition to the control microprocessor that controls the normal operation of the hair styling device, a dedicated safety microprocessor is used to run safety-critical software in order to prevent overheating.

[0134] Figure 9An exemplary implementation of this embodiment is shown. An array of heater electrodes 64 is provided. In this case, four heater electrodes 64a to 64d are provided, and one end of each heater electrode is connected to a DC power supply 509 that provides power to heat the heater electrode 64. The other end of each heater electrode 64 is connected to two MOSFET switches 504 and 506. For example, heater electrode 64a is connected to MOSFET switches 504a and 506a; heater electrode 64b is connected to MOSFET switches 504b and 506b, and so on. MOSFET switches 504 are controlled by a control microprocessor 512. For example, output 5 of control microprocessor 512 controls MOSFET switch 504a; output 6 of control microprocessor 512 controls MOSFET switch 504b, and so on. On the other hand, MOSFET switch 506 is controlled by a safety microprocessor 514. For example, output 5 of safety microprocessor 514 controls MOSFET switch 506a; output 6 of safety microprocessor 514 controls MOSFET switch 506b, and so on. The source terminals of MOSFET switch 504 are connected together and connected to ground via resistor R1 and the main MOSFET 516 (which is normally on and will be described in more detail below). The source terminals of MOSFET switch 506 are also connected together and connected to ground via resistor R2 (which may be the same as or different from resistor R1). Therefore, the heater electrodes 64 form a voltage divider circuit with resistor R1 and a second voltage divider circuit with resistor R2.

[0135] The control microprocessor 512 runs standard software to perform all temperature control and sensing functions. Specifically, the control microprocessor 512 controls MOSFET switches 504 to control the current flowing through the heater electrodes 64. In this embodiment, each heater electrode 64 is formed of a material whose resistance varies with temperature. As previously mentioned, this can be a PTC-type material or an NTC-type material. When the desired temperature of a heater electrode 64 is to be sensed, the control microprocessor 512 turns on the corresponding MOSFET switch 504 while isolating the other heater electrodes 64 from the resistor R1 by ensuring that their corresponding MOSFET switches 504 are turned off. Since each heater electrode 64 and the resistor R1 form a voltage divider, the voltage at the positive terminal of the operational amplifier 515-1 will depend on the temperature of the heater electrode 64. Therefore, the signal output from the comparator 515-1 will vary with the desired temperature of the heater electrode 64, and this sensor signal is fed back to the input of the control microprocessor 512. The control microprocessor 512 then cycles through each heater electrode 64 one at a time, connecting each heater electrode 64 to resistor R1 to obtain a temperature sensor signal for each heater electrode 64. As previously described, each temperature sensor signal from amplifier 515-1 can be converted into a corresponding temperature measurement via an appropriate formula or a suitable lookup table, or it can be used directly as input to the control loop calculations performed by the control microprocessor 512. This temperature sensor signal can be obtained simultaneously with or interleaved with powering the heater electrode 64 to heat the heater 6 for styling the user's hair. The control microprocessor 512 then uses the temperature sensor signal or converted temperature for each heater electrode 64 as part of a feedback loop to control the power supply to the heater electrodes 64, thereby maintaining a desired temperature for each heater electrode 64 (which may be the same for each heater electrode 64 or may be different for each heater electrode 64).

[0136] In addition to using a voltage divider formed between the respective heater electrode 64 and resistor R2, the safety microprocessor 514 performs a similar temperature sensing process on the heater electrode 64. When the safety microprocessor 514 wants to determine the desired temperature of the heater electrode 64, it turns on the corresponding MOSFET 506 while isolating the other heater electrodes 64 from resistor R2 by ensuring that its corresponding MOSFET switch 506 is turned off. Since each heater electrode 64 forms a voltage divider with resistor R2, the voltage at the positive terminal of amplifier 515-2 will depend on the temperature of the heater electrode 64. Therefore, the output signal of operational amplifier 515-2 will vary with the desired temperature of the heater electrode 64, and this output signal is fed back to the input of the safety microprocessor 514. The safety microprocessor 514 can then cycle through each heater electrode 64 one at a time, connecting each heater electrode 64 to resistor R2, thereby obtaining the temperature sensor signal of each heater electrode 64. This temperature sensor signal can be obtained simultaneously with or alternately with powering the heater electrode 64 to heat the heater 6 for styling the user's hair, and this temperature measurement can be performed simultaneously with or alternately with temperature sensing performed by the control microprocessor 512. The safety microprocessor 514 then uses the sensed temperature to monitor whether its temperature sensor signal exceeds the aforementioned trigger temperature T. trigger The safety microprocessor 514 detects that the temperature of any heater electrode 64 has exceeded the trigger temperature. If the safety microprocessor 514 detects that the temperature of any heater electrode 64 has exceeded the trigger temperature, the safety microprocessor outputs a control signal to turn off the main MOSFET 516 (which is normally turned on during normal operation). In this way, the safety microprocessor 514 disconnects the heater electrode 64 from ground via resistor R1. The safety microprocessor 514 also turns off MOSFET 516 to disconnect the heater electrode 64 from ground via resistor R2. Because the safety microprocessor does not run any other software, once it determines that one or more heater electrodes 64 have reached the trigger temperature, the safety microprocessor 514 can quickly take action to prevent current from flowing through the heater electrode 64, so that the heater electrode 64 will cool down and prevent any heater electrode 64 from becoming higher than the maximum allowable temperature T. max hot.

[0137] In summary, a safety circuit for a low-heat-capacity hair styling appliance is described. The safety circuit may rely on a deliberately designed weak link or temperature sensor, electronic circuitry that can remove power from the heater electrodes, and a dual-microprocessor design.

[0138] Example 6 – Printed and Laser-Calibrable Trapezoidal Thermistors

[0139] In a sixth embodiment, a novel thermistor arrangement is provided, comprising components that can be printed and calibrated to produce linear and nonlinear PTC and NTC thermistors, which can be used and operated as described, replacing any thermistors described in other embodiments, examples, and alternatives. Specifically, the thermistor can be used as a temperature sensor in a circuit to sense the temperature of a heater and / or the temperature of a user's hair in a hair drying and / or styling device, wherein the temperature is fed back to a controller that controls the power supplied to the heater; and / or it can be used as part of a safety (fuse) circuit system that disconnects the heater from the power supply circuit system in the event of overheating.

[0140] By using different calibration data (pre-determined experimentally) that correlate the signal value obtained from the thermistor with the sensed temperature, the measurement value obtained from the thermistor can be equated to the temperature of different objects, such as the temperature of the heater, the temperature of the hair contact surface, or even the temperature of the user's hair. A well-calibrated thermistor allows controllers of different hair styling devices to use the same calibration data. That is, each hair styling device (with its own thermistor) does not need to be individually calibrated to correlate the measurement obtained from its thermistor with the desired temperature value. Alternatively, the position of the thermistor in the layered heater stack can depend on the sensed temperature. Thus, for example, when the thermistor is part of circuitry for sensing and / or controlling the temperature of the user's hair, it can be placed in a layer closer to the hair contact surface, and when it is part of circuitry for sensing and / or controlling the temperature of the heater, it can be placed in a layer closer to the heater track.

[0141] Figure 10 An exemplary embodiment is shown, wherein a thermistor main line 1001 is provided as the positive terminal of the thermistor 1000, a thermistor main line 1002 is provided as the negative terminal of the thermistor 1000, and a plurality of thermistor calibration lines 1010 are connected in parallel with other thermistor calibration lines 1010 and connected in series with the two thermistor main lines 1001 and 1002. In this example, there are seven thermistor calibration lines 1010a to 1010g, but the minimum required number of thermistor calibration lines 1010 is two. Due to the trapezoidal arrangement, the total impedance of the thermistor 1000 at a given temperature can be calculated by the following equation: in, This represents the total impedance of the thermistor 1000 at a given temperature. This represents the impedance of the thermistor main wire 1001 at a given temperature. This represents the impedance of the thermistor main wire 1002 at a given temperature. This indicates the impedance of each thermistor calibration line in use.

[0142] Each of the thermistor main lines 1001 and 1002 and the thermistor calibration line 1010 can be printed, including by screen printing, or deposited onto the surface of the hair styling appliance or other suitable substrate to manufacture the thermistor 1000. For example, it can be used... Figure 10 The conductive or resistive paste, ink, and other printable materials in the illustrated configuration are used to print and cure each portion of the thermistor 1000. Specifically, the thermistor calibration line 1010 is printed and cured or otherwise produced in a manner that allows for easy cutting.

[0143] Once manufactured, the thermistor 1000 can be tested under known conditions to determine whether its impedance at a given temperature is within the expected tolerance range of the desired value. If the impedance of the thermistor 1000 is not within the expected tolerance range, one or more of the thermistor calibration lines 1010 can be disconnected as needed using a laser or other suitable tool to increase the thermistor's impedance at that temperature. If the impedance is too high, additional calibration lines 1010 can be printed, cured, and connected between the thermistor main lines 1001 and 1002 as needed to reduce the thermistor's impedance to within the expected tolerance range of the desired value. Using this method of cutting and generating calibration lines 1010, the impedance of each thermistor 1000 manufactured within the expected tolerance range of the desired value can be calibrated.

[0144] When the thermistor calibration line 1010 is disconnected, this might mean removing the entire thermistor calibration line from the circuit. However, it is not necessary to completely remove the thermistor calibration line 1010. It is sufficient to divide the thermistor calibration line into two or more parts so that the two main thermistor calibration lines 1001 and 1002 are not electrically connected to each other through the disconnected thermistor calibration line 1010. In other words, this introduces a “break” in the thermistor calibration line. This process effectively gives the thermistor calibration line a much larger impedance than it previously had, so even though one end of a portion of the thermistor calibration line remains connected to the main thermistor line, the other end will not be connected to any other part of the circuit, and is therefore simply an open circuit. Therefore, a disconnected thermistor calibration line can be considered as effectively removing the thermistor calibration line from the circuit.

[0145] Other cutting, grinding, or severing methods can also be used to create a break in the thermistor calibration line 1010 to calibrate the thermistor 1000. For example, while a laser can be used as part of an automated calibration process, a razor or other suitable scraper can be used to break the thermistor calibration line 1010.

[0146] When designing printed and laser-calibrated trapezoidal thermistors, there are multiple arrangements that can be used for the thermistor main lines 1001 and 1002 and the thermistor calibration line 1010. For example, the thermistor main lines 1001 and 1002 can both have a larger impedance than the thermistor calibration line 1010, which allows for finer tuning during the calibration process. Alternatively, the thermistor main lines 1001 and 1002 can have a smaller impedance than the thermistor calibration line 1010, which allows for more significant changes in impedance during the calibration process when needed. Of course, it may be possible and sometimes desirable to combine thermistor main lines 1001 and 1002 with larger and smaller impedances, as well as the thermistor calibration line 1010 with larger and smaller impedances, to provide the possibility of both fine-tuning and coarse-tuning of the thermistor impedance. This may be desirable when the printing process is not always reliable or accurate. This allows for the manufacture and calibration of printed and laser-calibrated trapezoidal thermistors without the need for costly printing solutions.

[0147] For simplicity, the following three examples of printed and laser-calibrated trapezoidal thermistors are given:

[0148] Examples 1 and 3 illustrate the following: a thermistor has an initial nominal impedance of approximately 10 Ω, but with different arrangements of calibration lines 1010 to achieve different ways of calibrating the thermistor 1000. However, in each case, the impedance variability is less than 1 Ω, meaning both can be fine-tuned. Example 2 is an example arrangement where most of the thermistor's impedance lies within the thermistor calibration lines 1010a to 1010g. The total impedance is approximately 1.5 Ω when all calibration lines 1010 are intact, but if all calibration lines except one 1010 are broken, the impedance can vary to approximately 10 Ω. Therefore, Example 2 shows an example arrangement that can be used with highly variable printed settings, as the total impedance of the thermistor in Example 3 can vary much more significantly than the total impedance of the thermistors in Examples 1 and 3.

[0149] As an example, if a thermistor is printed with two main thermistor lines and eight calibration lines, each main thermistor line having an impedance of 5Ω at 20°C and each calibration line having an impedance of 10Ω at 20°C, this will provide a total impedance of 11.25Ω at 20°C. However, if the desired impedance is 12Ω at 20°C, and the desired tolerance range is ±0.5Ω at 20°C, it will be necessary to disconnect several calibration lines. To fit the tolerance range, it would be reasonable to disconnect between 2 and 4 calibration lines to provide an impedance of 11.7Ω to 12.5Ω at 20°C. In this way, the same printing process can be used to provide a thermistor that can be calibrated to provide an impedance of 10.8Ω to 20Ω at 20°C. It is also possible that the printing process itself does not always reliably produce thermistors that meet the expected specifications. Taking Example 1 in the table above as an example, the expected impedance at 20°C would be 10.04Ω. However, if the actual measured impedance is 9.7Ω, and the expected impedance is 10 ± 0.1Ω, it can be determined that the thermistor calibration lines 1010a to 1010d are disconnected to increase the impedance. The impedance is then tested again to check if any further calibration is needed. Alternatively or additionally, it is also reasonable to disconnect one thermistor calibration line at a time and recheck the measured impedance. In this way, the impedance of each disconnected line can also be calculated, allowing for methods to check the accuracy of the printing process, and thus further determining whether the thermistor calibration lines should be disconnected or printed next, and which thermistor calibration lines should be disconnected or printed next.

[0150] Preferred heater and safety circuit system

[0151] Figure 11 An exploded cross-sectional perspective view of a preferred heater assembly for use in a hair styling device is shown, with an exploded transverse cross-sectional view of heater 1106 and heater carrier or substrate 1168 shown on the left and a perspective view of heater 1106 and heater carrier 1168 shown on the right. This heater can be used with any of the aforementioned safety circuits. As previously described, heater 1106 is formed of multiple discrete layers mechanically or chemically bonded together. These layers include: Layer 1181 is a low-friction coating that also provides electrical insulation. This layer can be formed, for example, by a ceramic coating or paint, and is applied directly to the heater electrode layer 1184. Layer 1181 is designed to have a dielectric breakdown strength of 500 volts and has a strength of 9.35 × 10⁻⁶. -4 KW -1 cm 2 and 0.8 KW -1 cm 2The thermal resistance between the hair contact surface of the heater (the upper surface of layer 1181) and the heater electrode provides the necessary electrical insulation while minimizing potential temperature drops through the coating 1181. Minimizing temperature drops through layer 1181 is important when the heater electrode is used for temperature sensing, as this will make the determined temperature closer to the actual temperature of the hair contact surface. A ceramic-based coating, such as Cerasol (a ceramic coating) with a thickness of approximately 30 μm to 45 μm, can provide this dielectric breakdown strength and has a strength of approximately 0.5 KW. -1 cm 2 Up to 0.6 KW -1 cm 2 The thermal resistance is low. Other materials (such as aluminum nitride) can provide the required dielectric breakdown strength while offering even lower thermal resistance. For example, a 30 μm layer of aluminum nitride can provide the required dielectric breakdown strength of 500 volts and has a thermal resistance of only 9.35 × 10⁻⁶. -4 KW -1 cm 2 The thermal resistance. However, for mass-produced devices such as hair stylers, the cost of aluminum nitride layers may be too high in practice.

[0152] Layer 1184 is the heater electrode layer, which carries the heater electrodes used to heat the different heating zones of the heater. The electrodes can be formed of any suitable conductive material, but stainless steel is preferred.

[0153] Layer 1187 is an insulating layer (e.g., made of polyimide) that provides electrical insulation between electrode layer 1184 and the underlying heat-diffusing layer 1188. Polyimide is a good choice for this insulating layer 1187.

[0154] Layer 1188 is the heat dissipation layer that carries the heat sink and fuse components discussed above.

[0155] Layer 1192 is an adhesive layer for bonding the flexible heater 1106 (formed by layers 1181, 1184, 1187 and 1188) to the rigid support 1168.

[0156] Figure 12a This is a perspective view taken from above, showing the flexible heater 1106 (layers 1181, 1184, 1187 and 1188 bonded together), the adhesive layer 1192 and the rigid support 1168. Figure 12b This is a view from below of the flexible heater 1106, the adhesive layer 1192, and the rigid support 1168. Figure 12bAs shown, the rigid support 1168 has honeycomb struts 1253 to provide rigidity while maintaining low weight. The rigid support 1168 also includes eight vents 1255 (the two at the ends are hidden by the honeycomb struts 2353). These vents are positioned relative to eight hot fuses mounted on layer 1188 of heater 1106. In this embodiment, there are sixteen heating zones, and each hot fuse provides overheat protection for two adjacent heating zones. Holes 1257 are disposed in adhesive layer 1192 surrounding the vents 1255 to ensure that the vents 1255 are not blocked by the adhesive.

[0157] Figure 13 This is a plan view of independently controllable heater electrodes 1364-1 to 1364-16 on heater electrode layer 1184, which defines sixteen heating regions 467 disposed therein. Each heater electrode 1364 is formed by orbitals of resistive material, the geometry (orbit width, thickness, length) and material of which are specified to achieve a desired resistance for a specific power supply voltage, thus providing a desired peak power for a given heating region. Each heater electrode 1364 can be formed into a serpentine pattern using chemical etching as a manufacturing process (but other manufacturing processes can also be used to form the heater electrodes 1364). More specifically, a solid layer of conductive material is disposed and then etched to form the different heater electrodes 1364. Figure 13 The dark areas shown are the boundaries between etched portions of the electrode layer between the white serpentine sections in the attached figure, where the white serpentine sections are the serpentine conductor paths that constitute heater electrodes 1364. In this illustrated example, each heater electrode 1364 meanders from the edge of heater 1106 to the centerline of heater 1106 and then returns to the starting edge of heater 1106 in a meandering path.

[0158] Adjacent heater electrodes 1364 share a common positive terminal (though in other embodiments they may be connected to a common ground terminal) to reduce the number of electrical connections required between the drive and control circuitry (not shown) and the heater 1106. The common positive terminal for the pairs of adjacent heater electrodes 1364 is connected back to the drive and control circuitry from the edge of the heater 1106. The other end of each heater electrode 1664 is connected to ground via a corresponding switch forming part of the drive and control circuitry to allow independent control of the current flowing through each heater electrode 1364. As those skilled in the art will appreciate, having such a common positive terminal (or ground) is not necessary, and each heater electrode 1364 may be physically isolated from all other heater electrodes 1664, in which case each end of each heater electrode 1364 would be connected back to the drive and control circuitry separately. Figure 13As shown, the electrode layer 1184 has twelve protrusions extending outward from its two longitudinal edges. These protrusions bend around the upper surface of the rigid support substrate 1168 to connect to the drive and control circuitry system. Sixteen of the total twenty-four protrusions contain grounding terminals for the heater electrodes 1364, and eight protrusions contain a common positive terminal for a pair of adjacent heater electrodes 1364.

[0159] The conductive material used in layer 1184 (for forming heater electrode 1364) is preferably a PTC or NTC material (e.g., stainless steel or copper), such that the resistance of heater electrode 1364 depends on its temperature, and therefore the temperature of heating region 467 can be determined by measuring the parameter that varies with the resistance of the corresponding heater electrode 1364.

[0160] Figure 14 The form of the heat dissipation layer 1188 used in this example is shown in more detail (viewed from below heater 1106). As shown, the heat dissipation layer 1188 comprises sixteen radiators 1491-1 to 1491-16, which are positioned to align with the corresponding heater electrodes 1364-1 to 1364-16. The radiators 1491 are formed of a thermally and electrically conductive material, such as copper. Each radiator 2591 (except for radiators 2591-1 and 2591-16) is electrically connected to an adjacent radiator at its corner portion. Each radiator 1491 is also electrically connected to at least one adjacent radiator 1491 via a fuse located between adjacent radiators. Dashed circle 1434 shows one of the locations where fuses are installed to electrically connect adjacent radiators 1491-3 and 1491-4. Heat sink 1491 is arranged such that when the fuse is in the appropriate position, there is an electrical connection (and thus a current path indicated by the dashed arrow) from the positive fuse connection 1436 coupled to heat sink 1491-1, through heat sink 1491-1 to 1491-16, and back to the negative fuse connection 1438 coupled to heat sink 1491-16. If one of the heating areas overheats and the corresponding fuse connection breaks, this current path is broken, and a controller or control circuit system (to which the positive fuse connection 2136 and the negative fuse connection 2138 are coupled) can detect this break in the current path (e.g., by applying voltage to the two fuse connections 1436 and 1438 and detecting the presence of current (if the fuse circuit is operating correctly) or the absence of current (meaning one or more fuses have blown)) and can take appropriate control actions, such as stopping or preventing power from being applied to the heater electrodes. The operation of the preferred control circuit system detecting fuse melting and taking control actions will be described in more detail later.

[0161] Figure 15a and Figure 15bThis is an enlarged perspective view of the fuse 1534 used to connect adjacent heat sinks 1491-3 and 1491-4 in this example. In this example, the fuse 1534 is formed of conductive solder material that electrically connects the adjacent heat sinks 1491-3 and 1491-4. The fuse material is located on and electrically bridges the solder resist layer 1541. Figure 15a The intact fuse is shown, allowing current to flow between adjacent heat sinks 1491-3 and 1491-4; Figure 15b This illustrates what happens when the welding material in the heating zone next to the molten wire 1534 overheats and melts. Specifically, as the welding material melts, it is repelled from the solder resist 1541 and forms droplets on the side where it will cool (once the power is removed from the heater) and solidify again. The solder resist 1541 is non-conductive, therefore when the welding material melts and leaves the solder resist 1541 (as... Figure 15b As shown), adjacent heat sinks 1491-3 and 1491-4 are electrically isolated from each other, thereby breaking the electrical connection between the two fuse connections 1436 and 1438. As described above, this disconnection of the electrical connection is detected by the control circuit system and is used to control (generally stop) the power supply to the heater electrode 1364.

[0162] Figure 16a and Figure 16b This is a cross-sectional view through the heater 1106 (showing electrode layer 1184, insulating layer 1187, and heat sink and fuse layer 1188), adhesive layer 1192, and support member 1168, illustrating the arrangement of the fuse 1534 and the corresponding vent 1255 as described above. Specifically, Figure 16a It is a cross-sectional view when fuse 1534 is intact, and Figure 16b This is a cross-sectional view when the fuse 1534 has melted and been removed from the solder resist 1541. As those skilled in the art will understand from Figure 16, the vent 1255 prevents pressure from hot air. An air bag 1644 is provided within the support 1168 to accommodate the fuse 1534.

[0163] Preferred drive and control circuit system

[0164] Figure 17 This is a schematic diagram showing how heater electrodes 1364 can be connected together and connected to drive circuit system 1723 and power supply 1721, illustrating a preferred safety circuit system from which power can be removed if any heater electrode 1364 overheats. Figure 17As shown, one end of each heater electrode 1364-1 to 1364-16 is connected to power supply 1721 via main switch 1751, and the other end is connected to corresponding switches (MOSFET switches in this case) 1795-1 to 1795-16. Switch 1795 is controlled by microprocessor 1729. When heater electrode 1364 needs to provide heat, the corresponding switch 1795 closes, thereby connecting heater electrode 1364 to ground via resistor 17R. As a result, current flows from power supply 1721 to ground, causing heater electrode 1364 to heat up (when main switch 1751 is closed). Microprocessor 1729 can independently control the position of each switch 1795, thereby allowing each heater electrode 1364 to be independently powered to reach its own desired setpoint temperature. Typically, the setpoint temperatures of the different heater electrodes 1364 will be the same.

[0165] When the temperature of the selected heating region 467 needs to be determined, the switch 1795 of the corresponding heater electrode 1364 is closed, and all other switches 1795 are opened. Thus, the selected heater electrode 1364 is connected in series with resistor 17R. Since the heater electrode 1364 is formed of PTC or NTC material, the resistance of which changes with the temperature of the heater electrode 1364, the microprocessor 1729 can determine the resistance of the selected heater electrode 1364 by measuring the voltage drop across resistor 17R (using operational amplifier 1797), and therefore determine the temperature of the corresponding heater electrode 1364. If the determined temperature is higher than the desired temperature of the heating region 467, the microprocessor 1729 can reduce the power applied to the heater electrode 1264; or if the heating region 467 is at a temperature lower than the desired temperature, the microprocessor 1729 can increase the power applied to the corresponding heater electrode 1364. Any suitable on / off control or PWM (pulse width modulation) control can be used to change the power applied to different heater electrodes 1364. The microprocessor 1729 can sequentially select each heater electrode 1364 to determine the temperature of each heater electrode 1364. Figure 17It is also shown that the voltage supplied to heater electrode 1364 can also be provided to microprocessor 1729 (if the voltage is greater than that acceptable to microprocessor 1729, it is provided to microprocessor 1729 via a suitable scaling or conversion circuitry system (not shown)). This voltage input allows microprocessor 1729 to regulate the drive of heater electrode 1364, for example, when powered by a battery and the battery is depleting. The voltage applied across the heater electrode may drop for other reasons, including voltage drop across the cable under high load, tolerances in the power supply output, etc. By measuring the applied voltage, microprocessor 1729 can use this information to more accurately calculate the resistance (and therefore the temperature of that heater electrode) of each heater electrode under given current circuit conditions. For example, microprocessor 1729 can use the measured voltage across resistor 17R to calculate the current flowing through heater electrode 1364 (by dividing the measured voltage across resistor 17R by the known resistance of resistor 17R). The microprocessor 1729 can then determine the resistance of the heater electrode 1364 by subtracting the voltage across resistor 17R from the sensed voltage applied to the heater electrode 1764 and dividing by the determined current. If necessary, the calculated resistance can then be equivalent to the temperature of the heater electrode 1764 using an appropriate lookup table.

[0166] Figure 17 It is also shown how the eight fuses 1534-1 to 1534-8 used in the preferred heater 1106 are connected to the control circuit system and how power can be automatically removed from the heater electrode 1364. Specifically, as Figure 17 As shown, the gate of the main switch 1751 is connected to the power supply via a voltage divider circuit 1756, which is connected to ground via a fuse 1534 and an optional test switch 1758. During normal operation, when the fuse 1534 is intact, the voltage at the gate of the main switch 1751 will be lower than the voltage at the source terminal of the main switch 1751. This means that the main switch 1751 is closed, and current can flow from the power supply 1721 through the main switch 1751 to the heater electrode 1364. However, if one or more fuses 1534 melt and disconnect the electrical connection between the voltage divider circuit 1756 and ground, the voltage at the gate of the main switch 1751 will become the same as the voltage at the source terminal of the main switch 1751, causing the main switch 1751 to open and thus isolating the heater electrode 1364 from the power supply 1721.

[0167] An optional test switch 1758 is configured to allow the microprocessor 1729 to test for faults in the circuitry system. Specifically, the main switch 1751 may malfunction and enter a permanently closed position. In this case, if one or more fuses 1534 melt and disconnect from ground, the main switch 1751 will not disconnect the connection between the power supply 1721 and the heater electrode 1364. However, by configuring the test switch 1758, which can be opened and closed by the microprocessor 1729, the microprocessor 1729 can check that the main switch 1751 has not malfunctioned and entered a permanently closed state. More specifically, when the microprocessor 1729 opens the test switch 1758, this simulates the breaking of one of the fuses 1534, which should disconnect the main switch 1751. The microprocessor 1729 can then monitor the temperature of one or more heater electrodes 1364 in the manner described above (using operational amplifier 1797). If the main switch 1751 operates correctly, the temperature of the monitored heater electrode 1364, or each monitored heater electrode 1364, should decrease (because the heater has a low heat capacity, so the decrease is rapid). If, after the test switch has been opened, the temperature of any monitored heater electrode 1364 remains above the threshold temperature, the microprocessor 1729 can assume that the main switch 1751 has failed in its closed state and can therefore open all switches 1795 to prevent further heating of the heater electrodes 1364.

[0168] like Figure 17 As shown, test switches 1758 and 1795 are n-channel MOSFETs, and the main switch 1751 is a p-channel MOSFET. The advantage of using n-channel switches is that they will enter an off state when power is removed from the control circuit, which should remove all power to the heater electrode 1364.

[0169] Replacement and modification

[0170] Various embodiments have been described above by way of example. As those skilled in the art will understand, various alternatives and modifications can be made to the above embodiments. Some of these alternatives and modifications will now be described.

[0171] The invention has been described above by way of implementation in a hair straightening device (“straightener”) employing a flat hair styling heater 6. However, the invention can alternatively be implemented in any form of hair styling device, such as (but not limited to) curling irons, hair clips, or hot brushes. The heater 6 may define a flat, curved, ridged, or barrel-shaped heating surface. The hair styling device may have two arms similar to the device shown in FIG. 1, or it may be a single-arm device.

[0172] In the above embodiments, the MOSFET switch is used to control the power supply and sensing of the heater electrodes. As those skilled in the art will understand, other switches may be used instead. For example, field-effect transistors (FETs), such as gallium nitride FETs or bipolar junction transistors (BJTs), may be used.

[0173] The switching device can be placed on the high side or low side of the heater's power supply.

[0174] In embodiments 4 and 5 described above, heater electrodes 64 are used for heating and temperature sensing. In alternative embodiments, separate temperature sensors may be provided for sensing the temperature of each heating region defined by the respective heater electrodes 64. For example, referring to FIG2, a separate temperature sensor layer may be provided below the dielectric layer 66 or on top of the layer 62.

[0175] In the above embodiments, a DC power supply is used to provide power for heating the heater electrode 64. This DC power supply is typically a battery, but a DC power supply that draws power from a mains AC signal can also be used. In embodiments where a separate temperature sensor is provided, the AC mains power supply can be used to heat the heater electrode. In this case, a thicker dielectric layer can be provided between the heater electrode 64 and the hair contact surface of the hair styler.

[0176] In an alternative to Embodiment 4 (implementing a dual-microprocessor system), the second separate microprocessor can be selected to be different from the first separate microprocessor. This can be a deliberate choice to avoid the possibility of repeating errors. In some possible implementations, the firmware may also be developed by a separate team to further minimize the possibility of any repeating firmware errors.

[0177] The above embodiments can be used alone or in any combination. For example, security solutions provided by electronic devices (such as embodiments 2 and 3) can be provided in combination with microprocessor-based security strategies (such as embodiments 4 and 5).

[0178] In hardware-only embodiments 1 to 3, the protection circuit system output can be monitored by the main CPU. Therefore, although the software does not directly involve over-temperature protection, the firmware can provide additional desired functionality, such as recording faults to non-volatile memory for later retrieval, or if the manufacturer requires an over-temperature fault to cause permanent disconnection of the heater, the recorded over-temperature fault stored in non-volatile memory can cause the MCU firmware to enter a permanent fault mode even after power cycling.

[0179] It should be understood that the permissible response time depends on the heating rate and the maximum permissible temperature T. max and trigger temperature T trigger For example, for 410°Cs -1The heating rate is set to 250℃. max and 240℃ T trigger It requires a (maximum) response time of 0.024 seconds. As another example, for 400°Cs... -1 The heating rate is set to 300℃. max and 240℃ T trigger It requires a (maximum) response time of 0.15 seconds.

[0180] It should also be noted that the weld link can be defined by its thickness rather than its weight. For example, the required thickness of the weld link can be determined by the following formula: Where Δz is the solder film thickness; Q is the energy flux; t is the allowable response time; L is the latent heat of fusion; and ρ is the density. In one example, the available heater flux is 20 W / cm². 2 The allowable response time is 0.3 s (as described above). If tin-based solder is used, the latent heat of fusion is 60 kJ / kg, and the density is 7300 kg / m³. 3 Therefore, for this example, a solder film thickness Δz of less than 0.011 mm may be required to achieve the desired response time. To account for the possibility that not all available heater flux enters the soldering link, it is preferable to achieve an even smaller thickness for the soldering link.

[0181] As another example, the weld link could be 1 mm × 0.5 mm × 0.25 mm in size and weigh approximately 0.002 g. The fuse could comprise a weld link formed of a tin-based alloy (such as SN95SB5), which is a tin-antimony alloy with a specific heat capacity of 0.23 kJ / kg K. Such a fuse is expected to melt within approximately 0.2 seconds; in other words, it has a response time of approximately 0.2 seconds (e.g., when it starts at 185°C and melts at 240°C).

[0182] In Example 6, the thermistor main lines and thermistor calibration lines are described as being printed and cured. Alternatively, all or some of the thermistor main lines and / or calibration lines may be constituted by other physical components (e.g., thermistors) connected as otherwise described in Example 6; and calibration is performed by removing the physical components from the thermistors.

[0183] In the preferred control circuit system described above, a fuse is coupled between the main switch and a reference potential (ground). As those skilled in circuit design will understand, the fuse can be coupled to the main switch in several different ways. For example, the fuse can be coupled between a power supply reference potential (e.g., 5V) and the control gate of a control switch, the output of which is connected to the control gate of the main switch. In this case, when one of the fuses melts, this disconnects the control switch from the reference potential, causing the control switch to change state, which in turn causes the main switch to change state, thereby preventing the supply of power to one or more of the heater electrodes. Of course, other arrangements are also possible.

[0184] In the preferred heater arrangement described above, eight fuses are provided to protect sixteen heating zones. As those skilled in the art will understand, one fuse can be provided for each heating zone, or in practice, one fuse can be provided for three or more heating zones. Since the heating zones are arranged along the length and width of the heater, providing one fuse for four heating zones will work well.

[0185] Each feature disclosed in the specification, (appropriate) claims, and drawings may be provided independently or in any suitable combination.

[0186] The reference numerals appearing in the claims are for illustrative purposes only and should not be construed as limiting the scope of the claims.

[0187] Undoubtedly, those skilled in the art will conceive of several other effective alternatives. It should be understood that the invention is not limited to the described embodiments, but includes modifications that are obvious to those skilled in the art and fall within the scope of the appended claims.

[0188] Throughout the description and claims of this specification, the words “comprising” and “including”, as well as variations thereof, mean “including but not limited to” and are not intended to exclude other components, integrals or steps.

[0189] Various examples have been described above. The following numbered clauses summarize one or more aspects of some of those examples:

[0190] Aspect 1

[0191] 1. A hair drying and / or styling apparatus, comprising a calibrated thermistor, wherein the calibrated thermistor includes: The main line of the first thermistor having a first impedance; The main line of the second thermistor with a second impedance; and Multiple thermistor calibration lines, each thermistor calibration line having its own impedance, wherein the multiple thermistor calibration lines are electrically connected in parallel with each other and electrically connected in series with a first thermistor main line and a second thermistor main line, wherein at least one of the multiple thermistor calibration lines is disconnected to provide the calibrated impedance of the calibrated thermistor.

[0192] 2. The apparatus according to Clause 1, wherein at least one of the first thermistor main line, the second thermistor main line, and a plurality of thermistor calibration lines is printed on the surface of a hair drying and / or styling apparatus or other substrate.

[0193] 3. The apparatus according to any one of the preceding clauses, wherein the first thermistor main line and the second thermistor main line have the same impedance.

[0194] 4. The apparatus according to any one of the preceding clauses, wherein at least two of the plurality of thermistor calibration lines have the same impedance when not disconnected.

[0195] 5. The apparatus according to any one of the preceding clauses, wherein at least two of the plurality of thermistor calibration lines have different impedances when not disconnected.

[0196] 6. The apparatus according to any one of the preceding clauses, wherein the impedance of at least one of the first thermistor main line and the second thermistor main line is lower than the impedance of at least one of the plurality of thermistor calibration lines.

[0197] 7. The apparatus according to any one of the preceding clauses, wherein the impedance of at least one of the first thermistor main line and the second thermistor main line is higher than the impedance of at least one of the plurality of thermistor calibration lines.

[0198] 8. The apparatus according to any one of the preceding clauses, wherein the plurality of thermistor calibration lines are individually disconnectable.

[0199] 9. The device according to any one of the preceding clauses, wherein the calibrated thermistor forms part of a thermal safety circuit for the heater of the hair styling device, or part of a sensor circuit for sensing and / or controlling the temperature of the heater of the hair styling device, or part of a sensor circuit for sensing and / or controlling the temperature of the user's hair.

[0200] 10. A method for manufacturing a hair drying and / or styling apparatus having a calibrated thermistor, the method comprising: Set a first thermistor main line with a first impedance; Set a second thermistor main line with a second impedance; Multiple thermistor calibration lines are provided, each thermistor calibration line having its own impedance, wherein the multiple thermistor calibration lines are electrically connected in parallel with each other and electrically connected in series with the first thermistor main line and the second thermistor line. The impedance of the thermistor is calibrated to be within the desired tolerance range of the desired impedance; and Integrate the calibrated thermistor into hair drying and / or styling devices.

[0201] 11. The method according to Clause 10, wherein calibrating the impedance of the thermistor to be within the desired tolerance of the desired impedance comprises: measuring the impedance of the thermistor at a set temperature and comparing the measured impedance with the desired impedance.

[0202] 12. The method according to Clause 11, wherein calibrating the thermistor further comprises: selecting at least one of a plurality of thermistor calibration lines based on a comparison of a measured impedance with a desired impedance; and disconnecting the selected at least one thermistor calibration line.

[0203] 13. The method according to Clause 12, wherein disconnecting the selected at least one thermistor calibration line comprises: using a laser to disconnect at least one thermistor calibration line.

[0204] 14. The method according to Clause 11, wherein calibrating the impedance of the thermistor to be within the desired tolerance of the desired impedance further comprises: determining, based on a comparison of the measured impedance with the desired impedance, to provide at least one additional thermistor calibration line; and At least one additional thermistor calibration line is printed in series with the first thermistor main line and the second thermistor main line.

[0205] Aspect 2

[0206] 1. A hair drying and / or styling appliance comprising a multilayer heater having multiple functional layers bonded together, wherein the multilayer heater is mounted within the appliance such that during user use of the appliance, hair contacts the hair contact surface of the multilayer heater and is heated by conduction, wherein the multilayer heater comprises: A heater electrode layer, comprising one or more heater electrodes formed of a conductive material, wherein the one or more heater electrodes generate heat when an electric current passes through them; and At least one upper dielectric layer is located above the heater electrode layer to be electrically insulated from the heater electrode layer; The upper surface of the dielectric layer provides a hair contact surface for the multilayer heater.

[0207] 2. The appliance according to Clause 1, wherein at least one dielectric layer is formed as a coating on the upper surface of the heater electrode layer.

[0208] 3. The apparatus according to Clause 2, wherein the coating is applied as a spray, paint, physical vapor deposition, sputtering or evaporation.

[0209] 4. The appliance according to any one of clauses 1 to 3, wherein the heater has a heating element greater than 2 W / cm². 2 And less than 100W / cm 2 Preferably greater than 8 W / cm 2 The power density.

[0210] 5. The appliance according to any one of clauses 1 to 4, wherein the dielectric layer is directly mounted on the upper surface of the heater electrode layer.

[0211] 6. The appliance according to any one of clauses 1 to 5, wherein one or more of the heater electrodes are formed of a conductive material whose resistance changes with the temperature of the heater, thereby enabling the temperature of the hair contact surface to be determined by measuring the resistance of one or more heater electrodes.

[0212] 7. The appliance according to any one of clauses 1 to 6, wherein the heater electrode layer comprises a plurality of independently controllable heater electrodes defining corresponding plurality of heating areas located on the hair contact surface of the multilayer heater.

[0213] 8. The appliance according to Clause 7, wherein a plurality of independently controllable heater electrodes are arranged in a two-dimensional array along the length and width of the heater.

[0214] 9. The appliance according to Clause 8, wherein a plurality of independently controllable heater electrodes are arranged in two rows extending along the length of the heater.

[0215] 10. The appliance according to any one of clauses 7 to 9, wherein the multilayer heater further comprises at least one heat dissipation layer disposed below the heater electrode layer.

[0216] 11. The appliance according to Clause 10, wherein the second dielectric layer is disposed between the heater electrode layer and the heat dissipation layer.

[0217] 12. The appliance according to clause 10 or 11, wherein the heat dissipation layer includes a plurality of heat sinks that regularize the heating provided in the heating area.

[0218] 13. The appliance described in Clause 12, when subordinate to Clause 8, wherein a radiator is provided for each row of independently controllable heater electrodes.

[0219] 14. The appliance according to Clause 12, wherein at least one heat sink is provided for each heater electrode.

[0220] 15. The appliance according to any one of clauses 12 to 14, wherein each radiator is formed as an island that does not contact adjacent radiators, so as to minimize heat diffusion from one heating zone to adjacent heating zones.

[0221] 16. The appliance according to any one of clauses 12 to 15, wherein each radiator is formed of metal.

[0222] 17. The appliance according to any one of clauses 12 to 16, wherein the heat sinks are isolated from each other in a plane perpendicular to the thickness by a solid or semi-solid material having a thermal conductivity of less than 35 W / mK, and preferably less than 0.3 W / mK.

[0223] 18. The appliance according to any one of the preceding clauses, wherein the multilayer heater further includes an auxiliary heater electrode layer, which includes one or more heater electrodes disposed below the heater electrode layer and a dielectric layer disposed between the heater electrode layer and the auxiliary heater electrode layer.

[0224] 19. The appliance according to any one of clauses 1 to 18, wherein the multilayer heater is flexible and bonded to a rigid structure to provide rigidity to the multilayer heater.

[0225] 20. The appliance according to any one of clauses 1 to 19, wherein the multilayer heater has a flat, curved and / or ribbed heating surface.

[0226] 21. The appliance according to any one of clauses 1 to 20, wherein the multilayer heater provides a flat heating surface and has curved edges that provide a curved heating surface.

[0227] 22. The appliance according to any one of clauses 1 to 21 further includes a controller configured to control the electrical application to the multilayer heater to control the heat generated by the multilayer heater.

[0228] 23. The appliance according to any one of clauses 1 to 22, wherein the appliance is a single-arm or double-arm device including a handle.

[0229] 24. The appliance according to any one of the preceding clauses, wherein the multilayer heater is flexible and mounted to a rigid support, wherein the ends of one or more heater electrodes are disposed on at least one connecting protrusion folded under the rigid support.

[0230] 25. The appliance according to any one of clauses 1 to 24, wherein the upper dielectric layer has a dielectric breakdown strength greater than 500 volts and a dielectric strength of 9.35 × 10⁻⁶ volts. -4 KW -1 cm 2 With 0.8 KW -1 cm 2 The thermal resistance between them.

[0231] 26. A method for manufacturing a hair drying and / or styling appliance, comprising: A multi-layer heater with multiple functional layers bonded together is provided; A multi-layer heater is installed in the appliance such that during user use of the appliance, hair comes into contact with the hair contact surface of the multi-layer heater and is heated by conduction; wherein, the multi-layer heater includes: A heater electrode layer is provided, comprising one or more heater electrodes formed of a conductive material, the one or more heater electrodes generating heat when an electric current passes through the one or more heater electrodes; and At least one upper dielectric layer is provided on the heater electrode layer to electrically isolate the heater electrode layer from the hair contact surface; The upper surface of the dielectric layer provides a hair contact surface for the multilayer heater.

[0232] Aspect 3

[0233] 1. A method for preparing a weak link for a secure circuit system, comprising: A first welding material is applied to form a first connector at the end of a first conductor and a second connector at the end of a second conductor, wherein the first welding material has a first melting temperature; A second welding material is applied to connect the first connector and the second connector, wherein the second welding material has a second melting temperature higher than the first melting temperature; and Heated to a temperature between the first melting temperature and the second melting temperature.

[0234] 2. The method according to Clause 1 further includes: depositing solder resist material in the region between the first conductor and the second conductor.

[0235] 3. The method according to Clause 1 or 2 further includes: depositing a solder resist material in the region of the second welding material.

[0236] 4. The method according to any one of clauses 1 to 3, wherein the first conductor and the second conductor are conductor traces, preferably conductor traces on a dielectric layer.

[0237] 5. The method according to any one of clauses 1 to 4, wherein the weak link is configured to be adjacent to the heater.

[0238] 6. The method according to any one of clauses 1 to 5 further includes connecting the weak link to a switch, preferably a control switch.

[0239] 7. The method according to any one of clauses 1 to 6, wherein the step is performed on a heater for hair drying and / or styling appliances, preferably on a dielectric layer or heat dissipation layer of the heater for hair drying and / or styling appliances.

[0240] 8. The method according to any one of clauses 1 to 7, wherein the end of the first conductor is the edge of a first conductive region constituting a heat sink, and the end of the second conductor is the edge of a second conductive region constituting a heat sink.

Claims

1. A hair drying and / or styling device, comprising: A heater for providing heat for drying and / or styling hair, the heater having a heating rate greater than 30°C / second; A power source, which provides power to the heater; as well as A safety circuit system for disconnecting the power supply from the heater in response to an overheat triggering event or a fault detection event; The safety circuit system is configured to disconnect the power supply from the heater during a period of 0.02 seconds to 2 seconds after the overheating trigger event or the fault detection event.

2. The hair drying and / or styling apparatus according to claim 1, wherein, The heater includes independently operable heater regions, and each heater region includes at least one independently operable heater electrode.

3. The hair drying and / or styling apparatus according to claim 2, wherein, The safety circuit system is configured to de-energize the heater based on the detection of the overheat trigger event or the fault detection event in any one (or more) of the heater areas, preferably to disconnect power to all heater electrodes based on the detection of the overheat trigger event or the fault detection event in any one (or more) of the heater areas.

4. The hair drying and / or styling apparatus according to any one of claims 1 to 3, wherein, The safety circuit system includes an array of temperature sensors and means for detecting whether any one (or more) of the temperature sensors indicates an overheating trigger event.

5. The hair drying and / or styling apparatus according to claim 4, wherein, At least one of the temperature sensor arrays is configured to be thermally connected to one or more heater regions of the heater, or wherein at least one of the temperature sensor arrays is configured to be thermally connected to each heater electrode of the heater.

6. The hair drying and / or styling apparatus according to any of the preceding claims, wherein, The safety circuit system includes at least one weak link configured to melt at a predetermined temperature indicating an overheating trigger event, thereby disconnecting the circuit.

7. The hair drying and / or styling apparatus according to claim 6, wherein, At least one weak link is configured to be thermally connected to one or more heater regions of the heater, such that the weak link is configured to melt when any of the corresponding heater regions exceeds the predetermined temperature, or wherein at least one weak link is configured to be thermally connected to each heater electrode of the heater, such that the weak link is configured to melt when the corresponding heater electrode exceeds the predetermined temperature.

8. The hair drying and / or styling apparatus according to claim 7, wherein, The safety circuit system is configured to disconnect power only to the corresponding heater region and / or heater electrodes in the event of at least one weak link melting.

9. The hair drying and / or styling apparatus according to any one of claims 6 to 8, wherein, The at least one weak link is configured to melt during a period between 0.02 seconds and 2 seconds of the overheat triggering event, preferably between 0.025 seconds and 1 second, and more preferably between 0.05 seconds and 0.6 seconds.

10. The hair drying and / or styling apparatus according to any one of claims 6 to 9, wherein, The mass of the at least one weak link is less than or equal to 0.1 grams, and preferably greater than or equal to 0.5 milligrams.

11. The hair drying and / or styling apparatus according to any one of claims 6 to 10, wherein, The at least one weak link comprises a first welding material having a first melting temperature and a second welding material having a second melting temperature, preferably wherein, The second melting temperature is higher than the first melting temperature, and the second welding material constitutes a connection between the first welding material and the electrical conductor of the circuit, preferably a physical connection and an electrical connection.

12. The hair drying and / or styling apparatus according to claim 11, wherein, The at least one weak link is deposited by heating to a temperature between the first melting temperature and the second melting temperature.

13. The hair drying and / or styling apparatus according to claim 11 or 12, wherein, The combined mass of the first welding material and the second welding material is less than or equal to 0.1 gram, and preferably greater than or equal to 0.5 milligrams.

14. The hair drying and / or styling apparatus according to any one of claims 6 to 13, wherein, The substrate on which the weak link is disposed has a solder resist coating to facilitate the removal of molten solder, thereby ensuring that the electrical connection is broken.

15. The hair drying and / or styling apparatus according to any one of claims 6 to 14, further comprising a microfluidic structure adjacent to the at least one weak link for guiding out molten material and thereby disconnecting the electrical connection.

16. The hair drying and / or styling apparatus according to any one of claims 6 to 15, wherein, The at least one weak link is elastically biased so that the electrical connection breaks upon melting.

17. The hair drying and / or styling apparatus according to any one of claims 6 to 16, wherein, The at least one weak link is connected to a switch, preferably wherein the switch is configured to de-energize the heater based on the melting of the at least one weak link.

18. The hair drying and / or styling apparatus according to any one of claims 6 to 17, wherein, The safety circuit system includes an array of weak links, wherein the weak links are connected in series to a switch, preferably wherein the switch is configured to de-energize the heater based on the melting of at least one weak link in the array of weak links.

19. The hair drying and / or styling apparatus according to any one of claims 6 to 18, wherein, The at least one weak link is coupled to a switch, whereby, in the event of melting of one or more of the at least one weak link, the switch is configured to change state and prevent power from being supplied to at least one heater electrode of the heater.

20. The hair drying and / or styling apparatus according to claim 19, wherein, The heater includes a plurality of heater electrodes, and wherein changing the state of the switch prevents power from being supplied to each of the heater electrodes.

21. The hair drying and / or styling apparatus according to claim 20, wherein, The at least one link is coupled between the control gate of the switch and the reference potential, such that melting of the at least one link decouples the control gate of the switch from the reference potential, thereby changing the state of the switch.

22. The hair drying and / or styling apparatus according to claim 21, wherein, The switch is a first switch, wherein a second switch is coupled between the control gate of the first switch and the reference potential, and wherein the controller is configured to operate the second switch to simulate the melting of the at least one link, thereby testing the operation of the first switch.

23. The hair drying and / or styling apparatus according to any of the preceding claims, wherein, The safety circuit system includes a nonlinear thermistor array in thermal contact with the heater assembly and means for detecting the voltage across the nonlinear thermistor array, wherein the safety circuit system is configured to cut off the power supply to the heater based on whether the voltage across the nonlinear thermistor array exceeds or falls below a threshold indicating an overheating trigger event.

24. The hair drying and / or styling apparatus according to claim 23, wherein, At least one of the nonlinear thermistors in the array is configured to be in thermal contact with one or more heater regions of the heater to monitor the temperature of the heater region, or wherein at least one of the nonlinear thermistors in the array is configured to be in thermal contact with each heater electrode of the heater to monitor the temperature of the heater electrode.

25. The hair drying and / or styling apparatus according to claim 23 or 24, wherein, The nonlinear thermistor array is connected in series.

26. The hair drying and / or styling apparatus according to any of the preceding claims, wherein, The safety circuit system includes a parallel array of temperature sensors and means for detecting whether the voltage of any one (or more) of the parallel array of temperature sensors exceeds or falls below a threshold indicating an overheating trigger event, wherein the safety circuit system is configured to cut off the power supply to the heater based on detecting that the voltage of any one (or more) of the parallel array of temperature sensors exceeds or falls below the threshold indicating an overheating trigger event.

27. The hair drying and / or styling apparatus according to claim 26, wherein, The safety circuit system includes a diode array and means for detecting the voltage output from the diode array, wherein each diode in the diode array is connected across a temperature sensor in a parallel array of temperature sensors, and wherein the safety circuit system is configured to cut off the power supply to the heater based on whether the voltage output from the diode array exceeds or falls below a threshold indicating an overheating trigger event.

28. The hair drying and / or styling apparatus according to claim 26 or 27, wherein, The safety circuit system includes a multiplexer for sampling voltage connected across the parallel array of the temperature sensors, wherein the safety circuit system is configured to cut off the power supply to the heater based on the sampled voltage of any one (or more) of the parallel array of temperature sensors exceeding or falling below a threshold indicating an overheating trigger event.

29. The hair drying and / or styling apparatus according to any of the preceding claims, wherein, The safety circuit system includes a first microprocessor and a second microprocessor, both of which are configured to run software that measures the temperature of the heater.

30. The hair drying and / or styling apparatus according to claim 29, wherein, The safety circuit system includes means for comparing outputs from the first microprocessor and the second microprocessor to detect fault detection events.

31. The hair drying and / or styling apparatus according to claim 29 or 30, wherein, The first microprocessor and the second microprocessor are configured to run the same software for measuring the temperature of the heater.

32. The hair drying and / or styling apparatus according to any one of claims 29 to 31, wherein, The safety circuit system includes a first connection and disconnect device connected in series with the second connection and disconnect device, wherein the first microprocessor controls the first connection and disconnect device and the second microprocessor controls the second connection and disconnect device, such that the outputs of the first microprocessor and the second microprocessor must be consistent to supply power to the heater.

33. The hair drying and / or styling apparatus according to any one of claims 29 to 32, wherein, The safety circuit system includes a first array of connection and disconnection devices and a second array of connection and disconnection devices, wherein a first microprocessor controls each of the first array of connection and disconnection devices, wherein a second microprocessor controls each of the second array of connection and disconnection devices, and wherein the heater includes an array of heater electrodes, each heater electrode being connected to a connection and disconnection device in the first array of connection and disconnection devices, the connection and disconnection devices in the first array of connection and disconnection devices being connected in series with the connection and disconnection devices in the second array of connection and disconnection devices, such that the outputs of the first microprocessor and the second microprocessor must be consistent for each heater electrode to ensure that the heater electrode is electrically connected to the power supply.

34. The hair drying and / or styling apparatus according to any one of claims 29 to 33, wherein, The safety circuit system includes means for comparing the outputs of the first microprocessor and the second microprocessor for each heater electrode of the heater, wherein if the first microprocessor and the second microprocessor are inconsistent for any one (or more) of the heater electrodes, the connection and disconnection means are configured to disconnect the power supply from the heater.

35. The hair drying and / or styling apparatus according to any one of claims 29 to 34, wherein, The output signals from the first microprocessor and the second microprocessor are configured to be fed into an XOR gate such that if the outputs of the first microprocessor and the second microprocessor are consistent (or / for example, identical), the XOR gate outputs logic low (0).

36. The hair drying and / or styling apparatus according to any one of claims 29 to 35, wherein, The safety circuit system includes a series of XOR gates, each corresponding to a heater electrode of the heater, wherein the first microprocessor and the second microprocessor are configured to be fed into each of the series of XOR gates for the respective heater electrode.

37. The hair drying and / or styling apparatus according to claim 36, wherein, The outputs of the series of XOR gates are output to one or more OR gates such that if the outputs of the first microprocessor and the second microprocessor are inconsistent for any one (or more) of the heater electrodes, the safety circuit outputs logic high (1).

38. The hair drying and / or styling apparatus according to claim 36 or 37, wherein, The outputs of the series of XOR gates are output to one or more OR gates such that if the outputs of the first microprocessor and the second microprocessor are consistent for the heater electrode, the safety circuit outputs logic low (0).

39. The hair drying and / or styling apparatus according to claim 29 or 30, wherein, The first microprocessor runs control software, and the second microprocessor runs security software.

40. The hair drying and / or styling apparatus according to claim 39, wherein, The safety circuit system includes means for sending temperature measurements to the first microprocessor and the second microprocessor.

41. The hair drying and / or styling apparatus according to claim 40, wherein, The first microprocessor is configured to control the heater based on the temperature measurement.

42. The hair drying and / or styling apparatus according to claim 40 or 41, wherein, The safety circuit system includes a main connection and disconnection device for disconnecting power to the heater, wherein the second microprocessor controls the main connection and disconnection device based on the temperature measurement.

43. The hair drying and / or styling apparatus according to any one of claims 40 to 42, wherein, The heating assembly includes at least one thermistor, and the means for transmitting temperature measurements includes means for measuring resistance.

44. The hair drying and / or styling apparatus according to any one of claims 39 to 43, wherein, The heater is connected to the first microprocessor via a first connection and disconnection device controlled by the first microprocessor, and the heater is connected to the second microprocessor via a second connection and disconnection device controlled by the second microprocessor.

45. The hair drying and / or styling apparatus according to claim 44, wherein, Each heater electrode of the heater is connected to the first microprocessor via a first connection and disconnection device controlled by the first microprocessor, and the heater is connected to the second microprocessor via a second connection and disconnection device controlled by the second microprocessor.

46. ​​The hair drying and / or styling apparatus according to claim 45, wherein, The first microprocessor is configured to control the first connection and disconnection device to individually supply power to each heater electrode in order to determine the temperature measurement of that heater electrode, and / or the second processor is configured to control the second connection and disconnection device to individually supply power to each heater electrode in order to determine the temperature measurement of that heater electrode.

47. The hair drying and / or styling apparatus according to any of the preceding claims, comprising a main connection and disconnection device for disconnecting power to the heater based on an overheat triggering event and / or a fault detection event.

48. The hair drying and / or styling apparatus according to any one of claims 32 to 47, wherein, The connection and disconnection device includes a switch, preferably a MOSFET switch.

49. The hair drying and / or styling apparatus according to any of the preceding claims further includes a latching circuit system configured to introduce a delay or a semi-permanent disconnection of the power supply from the heater after an overheating trigger event or a fault detection event has occurred.

50. The hair drying and / or styling apparatus according to any of the preceding claims, wherein, The safety circuit system includes a comparator for comparing a voltage with a threshold indicating an overheating trigger event or a fault detection event.

51. The hair drying and / or styling apparatus according to any of the preceding claims, wherein, The safety circuit system includes a switch for controlling the power supplied to the heater, preferably a MOSFET switch, and / or preferably wherein the output of the comparator controls the switch.

52. The hair drying and / or styling apparatus according to any of the preceding claims, wherein, The safety circuit system is configured to disconnect the power supply from the heater during a period of 0.025 seconds to 1 second, more preferably during a period of 0.05 seconds to 0.6 seconds.

53. A safety circuit system for hair styling tools, comprising a heater having a heating rate greater than 30°C / second, wherein, The safety circuit system is configured to disconnect (or cut off) the power supply to the heater during a period of 0.02 seconds to 2 seconds after an overheating trigger event or a fault detection event.

54. The safety circuit system according to claim 53, further comprising any one of the safety circuit system features according to any one of claims 1 to 52.

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