Hair styling appliance

Abstract

We describe a hair styling apparatus and method of heating a ceramic heater in a hair styling apparatus, the ceramic heater comprising a ceramic layer and a heating element thermally coupled to said ceramic layer, the method comprising: heating the ceramic layer in at least two successive phases, wherein in a first phase the ceramic layer is heated at a first rate of heating to a first temperature; pausing the heating of said ceramic layer at the first temperature; and wherein in a second phase the ceramic layer is heated at a second rate of heating from the first temperature to a second temperature.

Claims

1. A method of heating a ceramic heater in a hair styling apparatus, the ceramic heater comprising a ceramic layer and a heating element thermally coupled to said ceramic layer, the method comprising: heating said ceramic layer in at least two successive phases, wherein in a first phase said ceramic layer is heated at a first rate of heating to a first temperature; pausing said heating of said ceramic layer at said first temperature; and wherein in a second phase said ceramic layer is heated at a second rate of heating which is slower than said first rate of heating, from said first temperature to a second temperature.

2. A method as claimed in claim 1, wherein said second temperature is an operating temperature of said ceramic heater.

3. A method as claimed in claim 1, wherein said pausing is for a predetermined period of time of no more than one second.

4. A method as claimed in claim 1, wherein said pausing comprises substantially ceasing to apply electrical power to said ceramic heater.

5. A method as claimed in claim 1, wherein said ceramic has a thickness of between 0.2 mm and 1.0 mm.

6. A method as claimed in claim 1, wherein said first rate of heating achieves said first temperature in a range of thirteen to sixteen seconds.

7. A method as claimed in claim 1, wherein said first temperature is 140 C.20%.

8. A method as claimed in claim 1, wherein said operating temperature is at least 160 C.

9. A method as claimed in claim 1, wherein said operating temperature is at least 185 C.

10. A method as claimed in claim 1, wherein the ceramic heater is substantially planar.

11. A method as claimed in claim 1, wherein the ceramic heater is substantially tubular.

12. A hair styling appliance comprising a ceramic heater, the ceramic heater comprising a ceramic layer and a heating element coupled to said ceramic layer; a temperature sensor arranged to sense a temperature of said ceramic heater; and a controller configured to control heating of said ceramic heater, wherein the controller is configured to: control heating of said ceramic layer in at least two successive phases, wherein in a first phase said ceramic layer is heated at a first rate of heating to a first temperature; pause heating of said ceramic layer at said first temperature; and wherein in a second phase said ceramic layer is heated at a second rate of heating, slower than said first rate of heating, from said first temperature to a second temperature.

13. A method of inhibiting cracking of a single-sided ceramic heater of a hair styling appliance, the method comprising: providing the hair styling appliance with a single-sided ceramic heater, wherein said single-sided ceramic heater has a structure comprising a ceramic layer with an electrical conducting element on a first face of said ceramic layer, a second opposite face of said ceramic layer being mounted on and in thermal contact with a face of a heating layer or plate, wherein said ceramic layer lacks a heating layer or plate on said first face; and controlling electrical power applied to said ceramic heater to heat said heating layer or plate in at least two successive phases; wherein in a first phase a temperature of said heating layer or plate rises towards a knee point temperature and in a second phase a temperature of said heating layer or plate rises above said knee point temperature; and wherein said controlling comprises controlling said electrical power for said ceramic heating to control said temperature of said heating layer or plate to a first target rate of temperature rise during said first phase and controlling said electrical power for said ceramic heating to control said temperature of said heating layer or plate with a second rate of temperature rise during said second phase, wherein said second rate of temperature rise is slower than said first rate of temperature rise.

14. A method as claimed in claim 13 wherein said controlling in said second phase comprises: controlling said electrical power for said ceramic heating to control said temperature of said heating layer or plate to a second target rate of temperature rise during said second phase.

15. A method as claimed in claim 13, wherein said controlling further comprises pausing said heating between said first and second phases.

16. A method of inhibiting cracking a single-sided ceramic heater of a hair styling appliance, the method comprising: providing the hair styling appliance with a single-sided ceramic heater, wherein said single-sided ceramic heater has a structure comprising a ceramic layer with an electrical conducting element on a first face of said ceramic layer, a second opposite face of said ceramic layer being mounted on and in thermal contact with a face of a heating layer or plate, wherein said ceramic layer lacks a heating layer or plate on said first face of said ceramic heating; and controlling electrical power applied to said ceramic heating to heat said heating layer or plate in at least two successive phases; wherein in a first phase said controlling controls a rate of temperature rise of said heating layer or plate towards a first rate and wherein in a subsequent second phase said controlling controls said rate of temperature rise of said heating layer or plate towards a second, lower rate.

17. A hair styling appliance comprising: a single-sided ceramic heater, wherein said single-sided ceramic heater has a structure comprising a ceramic layer with an electrical conducting element on a first face of said ceramic layer, a second opposite face of said ceramic layer being mounted on and in thermal contact with a face of a heating layer or plate, wherein said ceramic layer lacks a heating layer or plate on said first face; and an electric controller to control electrical power applied to said ceramic heater to heat said heating layer or plate in at least two successive phases; wherein in a first phase a temperature of said heating layer or plate rises towards a knee point temperature and in a second phase a temperature of said heating layer or plate rises above said knee point temperature; and wherein said controlling comprises controlling said electrical power for said ceramic heater to control said temperature of said heating layer or plate to a first target rate of temperature rise during said first phase and controlling said electrical power for said ceramic heater to control said temperature of said heating layer or plate with a second rate of temperature rise during said second phase, wherein said second rate of temperature rise is slower than said first rate of temperature rise.

18. A hair styling appliance as claimed in claim 17, wherein said electronic controller is configured to pause said heating between said first and second phases.

19. A hair styling appliance as claimed in claim 17, wherein said heating layer is directly mounted on said ceramic layer.

20. A hair styling appliance as claimed in claim 17, wherein the ceramic layer is 0.6 mm thick20%.

21. A hair styling appliance comprising: a single-sided ceramic heater, wherein said single-sided ceramic heater has a structure comprising a ceramic layer with an electrical conducting element on a first face of said ceramic layer, a second opposite face of said ceramic layer being mounted on and in thermal contact with a face of a heating layer or plate, wherein said ceramic layer lacks a heating layer or plate on said first face; and an electrical controller to control electrical power applied to said ceramic heater to heat said heating layer or plate in at least two successive phases; wherein in a first phase said controlling controls a rate of temperature rise of said heating layer or plate towards a first rate and wherein in a subsequent second phase said controlling controls said rate of temperature rise of said heating layer or plate towards a second lower rate.

22. A method of heating a ceramic heater in a hair styling apparatus, the method comprising: providing the hair styling appliance with a single-sided ceramic heater, wherein said single-sided ceramic heater has a structure comprising a ceramic layer with an electrical conducting element on a first face of said ceramic layer, a second opposite face of said ceramic layer being mounted on and in thermal contact with a face of a heating layer or plate, wherein said ceramic layer lacks a heating layer or plate on said first face; and controlling electrical power applied to said ceramic heater to heat said heating layer or plate in at least two successive phases; wherein in a first phase a temperature of said heating layer or plate rises towards a knee point temperature and in a second phase a temperature of said heating layer or plate rises above said knee point temperature; and wherein said controlling comprises controlling said electrical power for said ceramic heater to control said temperature of said heating layer or plate to a first target rate of temperature rise during said first phase and controlling said electrical power for said ceramic heater to control said temperature of said heating layer or plate with a second rate of temperature rise during said second phase, wherein said second rate of temperature rise is slower than said first rate of temperature rise.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the invention and to show how it may be carried into effect reference shall now be made, by way of example only, to the accompanying drawings in which:

(2) FIG. 1 shows a first example of a hair straightener in a context of which embodiments of the invention may be employed;

(3) FIG. 2 shows an example of a crimping iron in a context of which embodiments of the invention may be employed;

(4) FIG. 3a shows, schematically, a vertical cross-section through a heater plate;

(5) FIG. 3b shows, schematically, a cross-section through a tubular heater;

(6) FIG. 3c shows, schematically, a cross-section through a variant of the tubular heater of FIG. 3b;

(7) FIG. 4 shows a graph of temperature against time illustrating a method according to an embodiment of the invention; and

(8) FIG. 5 shows a block diagram of an electronic control system which may be employed, for example, in the hair styling appliances of FIGS. 1 and 2 to implement an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(9) Referring to FIG. 3a, this shows a single-sided ceramic heater 300 comprising a metal, for example aluminium, heating plate 310 bearing a layer of ceramic 320, for example an oxide layer, on which is deposited an electrically conductive pattern 330 forming a heating element. The heating plate may incorporate a temperature sensor 340 such as a thermistor or thermocouple; alternatively the temperature sensor may be located elsewhere.

(10) In embodiments the thickness of the metal heating plate 310 may be of order 1-2 mm, and the thickness of the ceramic layer 320 may be of order 0.6 mm.

(11) In the example of FIG. 3a, the heating layers are plates arranged in a planar fashion. In a variant to this, the layers may be formed into a tubular arrangement, in particular tubular plates as shown in FIGS. 3b and 3c. In FIGS. 3b and 3c a tubular ceramic heater is used in which the heater is arranged into cylindrical layers with a heating element on one side of the ceramic.

(12) In FIG. 3b, the ceramic heater 400 comprises a metal heating layer 410 with an inner ceramic layer 420 with the heating element 430 deposited on the inner side of the ceramic tube.

(13) In FIG. 3c, the ceramic heater 450 comprises a metal heating layer 460 with an inner ceramic layer 470 with the heating element 480 deposited on the outer side of the ceramic tube. The heating element 480 is separated from the metal heating layer 460 by an non conductive dielectric 465.

(14) Referring next to FIG. 4, this shows a graph of temperature against time for the heating plate of FIG. 3a according to an embodiment of the invention adopting a two phase heating approach. This graph has a first phase in the region 0-A and a second phase in a region B-C. During the first phase of heating the electronic control system of the hair styling appliance controls the heater to provide a first, fast slew rate, and during the second phase heating is controlled to take place at a second, slower slew rate. The break point between the first and second phases defines a knee on the temperature-time curve. Although schematically illustrated by straight lines the skilled person will appreciate that, in practice, the temperature-time graph may deviate from the idealised illustration.

(15) During the first phase the appliance, more particularly, the heating plate, heats from room temperature to around 140 C. typically over 13-16 seconds. The second slew rate is lower and takes the heater up to a typical operating temperature in the region of 185 C. (temperate E, time C). Preferably there is a short interval, between points A and B in FIG. 4, where heating is temporarily halted (and the temperature may even fall slightly, as indicated by the dotted line). In embodiments this temporary pause may be less than 1 second. Such a pause allows the ceramic heating system to relax. In some embodiments more than one pause may be introduced, provided multiple opportunities for the creaming heating system to relax.

(16) As previously mentioned, a conventional heater has heating plates on both the top and bottom of the ceramic, and this mechanical constraint provides thermal stability. Without a heating plate on top the heater can curl and crack and therefore careful control of the temperature profile of the heating is important. Embodiments of the invention can increase the lifetime of a single-sided ceramic heater vary substantially, for example from thousands of cycles to tens of thousands of cycles, thus providing very substantial benefits in hair styling apparatus comprising one or more single-sided ceramic heating plates.

(17) FIG. 5 shows an embodiment of an electronic control system 500 which may be employed to implement the temperature-time control curve of FIG. 4.

(18) The system receives a power input 502 from, for example, a mains power supply, a low voltage power supply (DC or AC), or a battery such as a rechargeable battery. The power input is provided to a power supply unit 504 which provides low voltage DC power to a microcontroller 506 coupled to non-volatile memory 508 storing process of control code for a control algorithm, and to ram 510. An optional user interface 512 is also coupled to microcontroller 506, for example to provide one or more user controls and/or output indications such as a light or audible alert. The latter may be employed to indicate when the temperature of the heating plate has reached either or both of the knee point between the first and second heating phases, and the target operating temperature. The temperature sensor 340 at FIG. 3 also provides an input to microcontroller 506.

(19) The microcontroller provides a control output to one or more power control devices 514, for example power semiconductor switching devices which provide controlled power from input 502 to one or both heaters 516. In embodiments power control module 514 provides pulse width modulation control with a controllable proportion of a mains voltage duty cycle on-time to control the power to heaters 516. This, for example, in the first, high slew rate heating phase, say, a 25% on-time duty cycle may be employed, dropping to a 20% on-time duty cycle during the second heating phase.

(20) The processor control code stored in memory 508 implements a slew rate control procedure, for example by determining a slew rate of the measured temperature, comparing this against the target slew rate and providing an output control signal in response to the difference. The skilled person will appreciate that any of the wide range of different control algorithms may be employed for the control loop including, but not limited to, on-off control, and proportional control. Optionally the control loop may include a feed-forward element responsive to a further input parameter relating to the hair styling apparatus, for example to use the operation of the apparatus, to improve the temperature control.

(21) No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.