Safety circuitry

Abstract

Safety circuits are described for a low thermal mass hair styling appliance. The safety circuits can rely on intentionally weak links or temperature transducers, and electronic circuits that can remove power from the heater electrodes, and dual microprocessor designs.

Description

This invention describes a safety circuit for a low-heat-capacity hair styling appliance. 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. Abstract

Claims

Claims1 . A hair drying and / or styling device comprising: a heater for providing heat for drying and / or styling hair, the heater having a heat up rate greater than 30 °C per second; a power source for providing power to the heater; and safety circuitry for disconnecting the power source from the heater in response to an overheat trigger event or a fault detection event; wherein the safety circuitry is configured to disconnect the power source from the heater within a period between 0.02 and 2 seconds of the overheat trigger event or the fault detection event.

2. The hair drying and / or styling device of claim 1 , wherein the heater comprises independently operable heater zones, and wherein each heater zone comprises at least one independently operable heater electrode.

3. The hair drying and / or styling device of claim 2, wherein the safety circuitry is configured to disconnect power from the heater in dependence on detection of the overheat trigger event or the fault detection event in any one (or more) of the heater zones, preferably to disconnect power to all heater electrodes in dependence on detection of the overheat trigger event or the fault detection event in any one (or more) of the heater zones.

4. The hair drying and / or styling device of any of claims 1 to 3, wherein the safety circuitry comprises an array of temperature sensors, and a means for detecting if any one (or more) of the temperature sensors indicates an overheat trigger event.

5. The hair drying and / or styling device of claim 4, wherein at least one of the array of temperature sensors is provided in thermal connection to one or more heater zones of the heater, or wherein at least one of the array of temperature sensors is provided in thermal connection to each heater electrode of the heater.

6. The hair drying and / or styling device of any preceding claim, wherein the safety circuitry comprises at least one weak link configured to melt at a predetermined temperature indicative of an overheat trigger event, thereby breaking the circuit.

7. The hair drying and / or styling device of claim 6, wherein at least one weak link is provided in thermal connection with one or more heater zones of the heater such that the weak link is configured to melt if any of the corresponding heater zones exceeds the predetermined temperature, or wherein at least one weak link is provided in thermal connection with each heater electrode of the heater such that the weak link is configured to melt if the corresponding heater electrode exceeds the predetermined temperature.

8. The hair drying and / or styling device of claim 7, wherein the safety circuitry is configured to disconnect the power only to the corresponding heater zone and / or heater electrode in dependence on at least one weak link melting.

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

10. The hair drying and / or styling device of any of claims 6 to 9, wherein the at least one weak link has a mass less than or equal to 0.1 gram, and preferably greater than or equal to 0.5 milligrams.11 . The hair drying and / or styling device of any of claims 6 to 10, wherein the 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 higher than the first melting temperature and the second solder material forms a connection between the first solder material and electrical conductors of the circuit, preferably a physical and electrical connection.

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

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

14. The hair drying and / or styling device of any of claims 6 to 13, wherein a substrate on which the weak link is provided has a coating of solder resist to facilitate removal of melted solder to ensure a break in electrical connection.

15. The hair drying and / or styling device of any of claims 6 to 14, further comprising microfluidic structures located adjacent the at least one weak link for channeling molten material away, and thereby break electrical connection.

16. The hair drying and / or styling device of any of claims 6 to 15, wherein the at least one weak link is resiliently biased such that electrical connection is broken upon melting.

17. The hair drying and / or styling device of any of claims 6 to 16, wherein the at least one weak link is connected to a switch, preferably wherein the switch is configured to disconnect power from the heater in dependence on the at least one weak link melting.

18. The hair drying and / or styling device of any of claims 6 to 17, wherein the safety circuitry comprises an array of weak links, wherein the weak links are connected in series to a switch, preferably wherein the switch is configured to disconnect power from the heater in dependence on at least one weak link of the array of weak links melting.

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

20. The hair drying and / or styling device of claim 19, wherein the heater comprises a plurality of heater electrodes and wherein the change of state of the switch prevents power being provided to each of the heater electrodes.

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

22. The hair drying and / or styling device of 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 a controller is configured to operate the second switch to simulate a melting of the at least one link to test the operation of the first switch.

23. The hair drying and / or styling device of any preceding claim, wherein the safety circuitry comprises an array of non-linear thermistors in thermal contact with the heater assembly, and a means for detecting a voltage across the array of non-linear thermistors, wherein the safety circuitry is configured to cut power supply to the heater in dependence on the voltage across the array of non-linear thermistors exceeding or falling below a threshold value indicative of an overheat trigger event.

24. The hair drying and / or styling device of claim 23, wherein at least one of the array of nonlinear thermistors is provided in thermal contact with one or more heater zones of the heater for monitoring the temperature of that heater zone, or wherein at least one of the array of non-linear thermistors is provided in thermal contact with each heater electrode of the heater for monitoring the temperature of that heater electrode.

25. The hair drying and / or styling device of claim 23 or 24, wherein the array of non-linear thermistors is connected in series.

26. The hair drying and / or styling device of any preceding claim, wherein the safety circuitry comprises a parallel array of temperature sensors, and a means for detecting if the voltage of any one (or more) of the parallel array of temperature sensors exceeds or falls below a threshold value indicative of an overheat trigger event, wherein the safety circuitry is configured to cut power supply to the heater in dependence on detection of a voltage of any one (or more) of the parallel array of temperature sensors exceeding or falling below a threshold value indicative of an overheat trigger event.

27. The hair drying and / or styling device of claim 26, wherein the safety circuitry comprises an array of diodes, wherein each of the array of diodes is connected across one of the parallel array of temperature sensors, and a means for detecting the voltage output from the array of diodes, wherein the safety circuitry is configured to cut power supply to the heater in dependence on the voltage output from the array of diodes exceeding or falling below a threshold value indicative of an overheat trigger event.

28. The hair drying and / or styling device of claim 26 or 27, wherein the safety circuitry comprises a multiplexer connected across the parallel array of temperature sensors for sampling thevoltages, wherein the safety circuitry is configured to cut power supply to the heater in dependence on the sampled voltage of any one (or more) of the parallel array of temperature sensors exceeding or falling below a threshold value indicative of an overheat trigger event.

29. The hair drying and / or styling device of any preceding claim, wherein the safety circuitry comprises a first microprocessor and a second microprocessor, both configured to run software measuring temperature of the heater.

30. The hair drying and / or styling device of claim 29, wherein the safety circuitry comprises means for comparing outputs from the first microprocessor and the second microprocessor to detect a fault detection event.31 . The hair drying and / or styling device of claim 29 or 30, wherein the first microprocessor and second microprocessor are configured to run identical software measuring heater temperature.

32. The hair drying and / or styling device of any of claims 29 to 31 , wherein the safety circuitry comprises a first connection and disconnection means in series with a second connection and disconnection means, wherein the first microprocessor controls the first connection and disconnection means and the second microprocessor controls the second connection and disconnection means, such that the outputs of the first microprocessor and second microprocessor must agree for power to be supplied to the heater.

33. The hair drying and / or styling device of any of claims 29 to 32, wherein the safety circuitry comprises a first array of connection and disconnection means, wherein the first microprocessor controls each of the first array of connection and disconnection means, and a second array of connection and disconnection means, wherein the second microprocessor controls each of the second array of connection and disconnection means, and wherein the heater comprises an array of heater electrodes, each heater electrode being connected to a connection and disconnection means of the first array of connection and disconnection means in series with a connection and disconnection means of the second array of connection and disconnection means, such that the outputs of the first microprocessor and second microprocessor must agree for each heater electrode for that heater electrode and the power source to be in electrical connection.

34. The hair drying and / or styling device of any of claims 29 to 33, wherein the safety circuitry comprises means for comparing outputs of the first microprocessor and the second microprocessor for each heater electrode of the heater, wherein a connection and disconnection means is configured to disconnect the power source from the heater if the first microprocessor and the second microprocessor disagree for any one (or more) of the heater electrodes.

35. The hair drying and / or styling device of any of claims 29 to 34, wherein output signals from the first microprocessor and the second microprocessor are configured to feed into an XOR gate, such that if the outputs of first microprocessor and the second microprocessor agree (or / for example, are the same) the XOR gate outputs a logical low (0).

36. The hair drying and / or styling device of any of claims 29 to 35, wherein the safety circuitry comprises a series of XOR gates, each XOR gate corresponding to a heater electrode of theheater, wherein the first microprocessor and the second microprocessor are configured to feed into each of the series of XOR gates in respect of the relevant heater electrode.

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

38. The hair drying and / or styling device of claim 36 or 37, wherein the outputs of the series of XOR gates are output into one or more OR gates such that if the outputs of the first microprocessor and the second microprocessor for the heater electrodes agree, the safety circuit outputs a logical low (0).

39. The hair drying and / or styling device of claim 29 or 30, wherein the first microprocessor runs control software and the second microprocessor runs safety software.

40. The hair drying and / or styling device of claim 39, wherein the safety circuitry comprises means for sending temperature measurements to the first microprocessor and the second microprocessor.41 . The hair drying and / or styling device of claim 40, wherein the first microprocessor is configured to control the heater in dependence on the temperature measurements.

42. The hair drying and / or styling device of claim 40 or 41 , wherein the safety circuitry comprises a master connection and disconnection means for disconnecting power to the heater, wherein the second microprocessor controls the master connection and disconnection means in dependence on the temperature measurements.

43. The hair drying and / or styling device of any of claims 40 to 42, wherein the heating assembly comprises at least one thermistor and the means for sending temperature measurements comprises a means for measuring resistance.

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

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

46. The hair drying and / or styling device of claim 45, wherein the first microprocessor is configured to control the first connection and disconnection means to provide power to each heater electrode individually in order to determine temperature measurements for that heater electrode and / or the second processor is configured to control the second connection and disconnection means toprovide power to each heater electrode individually in order to determine temperature measurements for that heater electrode.

47. The hair drying and / or styling device of any preceding claim, comprising a master connection and disconnection means for disconnecting power to the heater in dependence on an overheat trigger event and / or fault detection event.

48. The hair drying and / or styling device of any of claims 32 to 47, wherein the connection and disconnection means comprise a switch, preferably a MOSFET switch.

49. The hair drying and / or styling device of any preceding claim, further comprising latching circuitry configured to introduce a delay or a semi-permanent disconnection of the power source from the heater after an overheat trigger event or a fault detection event has occurred.

50. The hair drying and / or styling device of any preceding claim, wherein the safety circuitry comprises a comparator for comparing a voltage to a threshold value indicative of an overheat trigger event or a fault detection event.

51. The hair drying and / or styling device of any preceding claim, wherein the safety circuitry comprises a switch for controlling 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 device of any preceding claim, wherein the safety circuitry is configured to disconnect the power source from the heater within a period between 0.025 and 1 seconds, and more preferably between 0.05 and 0.6 seconds.

53. Safety circuitry for a hair styling appliance comprising a heater with a heat up rate greater than 30 °C per second, wherein the safety circuitry is configured to disconnect (or cut) power supply to the heater within a period between 0.02 and 2 seconds of an overheat trigger event or a fault detection event.

54. The safety circuitry of claim 53, further comprising any of the safety circuitry features of any of claims 1 to 52.

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