EP4687573A1

EP4687573A1 - A hair curler

Info

Publication number: EP4687573A1
Application number: EP24713436.4A
Authority: EP
Inventors: Jun Zhang; Chak Yuen LAW; Ou JIANG; Wai Ho LI
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2023-03-31
Filing date: 2024-03-19
Publication date: 2026-02-11
Also published as: JP2026502302A; CN120882338A; WO2024200081A1; KR20250165648A

Abstract

A hair curler has a heating barrel with an adjustable size. The heater of the heating barrel is controlled in dependence on the selected size of the heating barrel, such that a heating temperature and/or a heating duration applied to hair wound around the heating barrel is inversely correlated with the size of the barrel. In this way, the type of heating matches the curl size selected by the user.

Description

A HAIR CURLER

FIELD OF THE INVENTION

This invention relates to hair curlers, and in particular it relates to hair curlers in which hair is wound around a drum, and wherein there is an adjustable drum size.

BACKGROUND OF THE INVENTION

To meet different consumer needs, some consumer products may comprise an adjustable function to the user. This adjustable function may be realized by providing a changeable component, for example, the size, shape or other configuration of a certain component of the product is changeable.

For example, a hair curler is a handheld electronic product used to curl the hair. Its main components are a handle and a heating element. The heating element is in the form of a heating barrel which generally has a cylindrical shape. The heating barrel is for example a tourmaline ceramic panel.

It is known to provide a curler which enables the user to achieve different hair curl styles by providing a changeable heating element, in particular with a changeable heating barrel size. When the user wants to change their curling style, for example between larger curls and smaller curls, he/she typically operates a manual user interface such as a slider knob to drive the barrel size adjustment mechanism. Then, the barrel size changes accordingly.

Typically, the control of the heating barrel is independent of the selected barrel size. Indeed, the barrel size adjustment mechanism is for example purely mechanical, so that there are no control signals or sensing signals associated with the different barrel sizes.

It would be desirable to give more functionality to the user, to match their desired curl characteristics.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention, there is provided a hair curler, comprising: a heating barrel around which hair is to be wound for curling and comprising a heater; a barrel size changing mechanism adapted to change the size of the heating barrel in response to user input; and a controller adapted to control the heater in dependence on the selected size of the heating barrel, such that a heating temperature and/or a heating duration applied to hair wound around the heating barrel is inversely correlated with the size of the barrel.

This invention aims to implement heating control in dependence on the size of the curl selected by the user, when using an adjustable size curler. The invention is based on the insight that a user typically likes a loose curl effect if they select a large curl size, and a tight curl effect if they select small curl size. With this insight, and the knowledge that loose curls need less heat energy (in particular a lower temperature and/or a shorter heating time) and tight curls need more heat energy (in particular a higher temperature and/or a longer heating time), the invention proposes a heating control based on the curl size, in particular with lower heating energy (lower temperature and/or shorter heating time) for large curls than for small curls.

It is noted that the heating temperature may not be constant over time. In such a case, the heating temperature may be taken to be the average heating temperature over the heating time period. The heating time period is the time during which heat is applied to a particular section of hair while it is being curled (rather than the overall time for the complete curling process, which will of course depend on the amount of hair the user has chosen to curl, and the length of their hair). The section of hair being curled is the hair which is rotated around the heating barrel at a given time, in order for the curling function to be applied.

The heating barrel is a component with a changeable status, in particular size, and the barrel size changing mechanism is thus a status changing unit for changing the status of the component. The barrel size changing mechanism includes a user operation unit, and it is for example movable along a path between the operative positions. The barrel size changing mechanism changes the status of the component (the heating barrel) in response to the user operating the user operation unit (the selector).

The controller is for example adapted to control the heater such that a heating temperature is inversely correlated with the size of the barrel. Thus, a temperature control loop may be used to control the heater. The hair curler may then comprise a plurality of selectable heating barrel sizes, each having an associated temperature setting. The controller may be adapted additionally or alternatively to control the heater such that a heating time is inversely correlated with the size of the barrel. Thus, a same temperature may be applied for a shorter duration, or a lower temperature may be applied for a shorter duration (for larger curls). The hair curler may then comprise a plurality of selectable heating barrel sizes, each having an associated heating duration.

Each heating barrel size may be associated with a particular combination of heating temperature and heating time, for each curling operation.

The hair curler may comprise a sensor for sensing the selected size of the heating barrel for providing selected size information to the controller.

The sensor may be located at any location of the barrel size changing mechanism where the barrel size can be sensed, for example at any location along the drive chain between (i) a selector (i.e., a user operation unit) at which the user input is received for changing the heating barrel size and (ii) the heating barrel. For example, there may be a gear to drive the barrel to its different sizes and the sensor may be associated with the gear for detecting a gear position.

The sensing may be based on electrical contacts (which change configuration when the heating barrel size is changed) or magnetic sensing (wherein a magnetic coupling changes when the heating barrel size is changed) or based on capacitive sensing or resistance sensing (wherein a resistance or capacitance changes when the heating barrel size is changed) or based on optical sensing (wherein an optical path changes when the heating barrel size is changed). Thus, any suitable characteristic may be sensed that is indicative of the selected heating barrel size.

The barrel size changing mechanism for example comprises a manually- operated selector which has a plurality of operative positions, such that the heating barrel can be driven to different sizes using the manually-operated selector in response to the user input, each different size associated with one of the operative positions of the manually-operated selector, wherein the sensor is coupled with the manually-operated selector for sensing the position of the manually-operated selector and providing a signal indicating the operative position of the manually-operated selector to the controller.

The barrel size is in this example adjustable by the user operating a manually- operated selector. The selector then operates a mechanical structure for changing the barrel size, by a mechanical coupling. Thus, the barrel size is adjusted by a mechanical mechanism, which is actuated by the physical configuration of the selector. Thus, the control of the barrel size is purely mechanical, rather than using conversion of a user input into an electrical signal and then controlling an electrical actuator to change the barrel size. This mechanical system thus does not provide any electrical sensing signal. The sensing unit provides a suitable electrical signal to enable the operation of the curler to be adapted according to the selected curl size. The sensing unit is associated with the manual selector to sense the configuration (e.g., linear or rotational position) of the operation unit instead of sensing the actual change of the barrel size.

The manually-operated selector for example comprises a slider switch or a rotatable knob or a push-button.

Instead of sensing the barrel size, the hair curler may comprise: an electrical user interface for receiving the user input and generating a control signal; and an electrical actuator for controlling the barrel size changing mechanism in response to the control signal, wherein the control signal is provided to the controller for controlling the heater.

The curler for example comprises a motor to drive the barrel size changing mechanism, and the motor control signal can also be used by the controller as the heating control signal.

The heating barrel for example comprises a plurality of segments which are configurable to form a shape of different size depending on the user input. The shape in different size may be a closed or semi-closed, cylindrical, elliptic column shape or any other curved column shape. The heating barrel thus contracts or expands to the desired size.

The invention for example comprises a method of controlling a hair curler, the hair curler comprising a heating barrel around which hair is to be wound for curling and comprising a heater and a barrel size changing mechanism adapted to change the size of the heating barrel in response to user input, wherein the method comprises: controlling the heater in dependence on the selected size of the heating barrel, such that a heating temperature and/or a heating duration applied to hair wound around the heating barrel is inversely correlated with the size of the barrel.

The method may comprise controlling the heater such that a heating temperature is inversely correlated with the size of the barrel.

The method may additionally or alternatively comprise controlling the heater such that a heating time is inversely correlated with the size of the barrel. The invention also provides a computer program comprising computer program code which is adapted, when said program is run on a computer, to implement the method defined above.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows an example of the type of hair curler to which the invention may be applied;

Figure 2 shows one example of a known mechanical barrel size changing mechanism;

Figure 3 shows a cross section of the heating barrel and shows that it is formed of three segments;

Figure 4 shows a first implementation of a sensor;

Figure 5 shows a slider knob mounted over a Hall sensor to implement the sensor of Figure 4;

Figure 6 shows a second implementation of a sensor;

Figure 7 shows a third implementation of a sensor;

Figure 8 shows signals from the sensor of Figure 7 being provided to the controller; and

Figure 9 shows a method of controlling the hair curler described above.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention will be described with reference to the Figures.

It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

The invention provides a hair curler with a heating barrel having an adjustable size. The heater of the heating barrel is controlled in dependence on the selected size of the heating barrel, such that a heating temperature and/or a heating duration applied to hair wound around the heating barrel is inversely correlated with the size of the barrel. In this way, the type of heating matches the curl size selected by the user.

Figure 1 shows an example of the type of hair curler 10 to which the invention may be applied.

The hair curler 10 comprises a main body 12 having a handle 14 and a hair curling head 16. The hair curling head comprises a central cylindrical heating barrel 18 around which a shroud 20 extends. The shroud has a lateral opening 22 into which hair can be received. The received hair is wound around the heating barrel 18 by a looper 24, i.e., a rotatable element such as having a blade form. The looper 24 is driven to rotate around the heating barrel and it winds hair around the heating barrel. The hair between the heating barrel 18 and the shroud 20 is heated while in a wound condition.

The heating barrel comprises an internal heater (not shown) for heating an outer surface of the barrel, which will be in contact with hair wound around the barrel.

The hair curler has a controller 30 to control the temperature of the heater, which can evenly disperse the heat, circulate the heating process, improve the protein structure of the hair to create bends, and meanwhile protect the hair during the curling process.

This invention relates to hair curlers with an adjustable heating barrel size.

For this purpose, the hair curler comprises the heating barrel 18 around which hair is to be wound for curling and comprising an internal heater (as mentioned above) and also a barrel size changing mechanism adapted to change the size of the heating barrel in response to user input. Figure 1 shows a selector 32 to enable a user to select the heating barrel size. As explained below, in some examples the selector 32 may implement a purely mechanical adjustment of the heating barrel configuration, but in other examples an electrical actuation system may be used.

Figure 2 shows one example of a known mechanical barrel size changing mechanism. The size of the heating barrel 18 is changed by a rotary knob 40 which rotates a control disc 42. The control disc 42 engages with the barrel to move barrel sections together and apart and thereby change the outer diameter of the heating barrel, so that the radius of curls applied to the hair is changed.

Figure 3 shows a cross section of the heating barrel and shows that it is formed of three segments 50, 52, 54. They are slidably coupled together so that the three segments can be in a contracted state shown in Figure 3 A, a middle state shown in Figure 3B or an expanded state shown in Figure 3C. Each section has its own heater 50a, 52a, 54a. In general, the heating barrel comprises a plurality of segments which are configurable to form a shape of different size depending on the user input. The heating barrel thus contracts or expands to the desired size. The segments are driven together and apart by actuating drive pins 56. The example of Figure 3 is taken from CN218527966U to which reference is made for further explanation. CN218527966U is incorporated by reference.

However, any suitable expandable design of the heating barrel may be used.

Figure 2 shows an adjustment knob. In more general terms, a status changing unit is provided which comprises a user operation unit (functioning as a user interface) movable along a path. The heating barrel size changing mechanism changes the barrel size in response to the user operating the user interface. Instead of a rotary knob, the user operation unit may be a sliding button or a switch.

One aspect of this disclosure is based on the recognition that in known designs the same heating parameters are kept for different heating barrel sizes during hair styling. This may overheat the hair or the heating may be insufficient to provide the desired hair style. Therefore, the first aspect of this disclosure is to provide a different heating time and/or a different temperature for different heating barrel sizes during the hair curling process. Thus, the heating time and/or heating temperature of the heater are controlled in dependence on the heating barrel size.

For this purpose, the controller is adapted to control the heater in dependence on the selected size of the heating barrel, such that a heating temperature and/or a heating duration applied to hair that is wound around the heating barrel is inversely correlated with the size of the barrel.

This inverse correlation does not need to be linear. Typically, there will be a set of heating barrel sizes, such as a fixed set of diameters between 25mm and 35mm. Each allowable barrel size may be associated with a particular heating temperature and a particular heating time. There is feedback to the user when the heating time (known as the styling time) is finished to alert user to pull the curler off the curls or pull curled hair from the curler. The feedback is for example an audible signal such as a buzzer.

A user typically likes a loose curl effect if they select a large curl size, and a tight curl effect if they select small curl size. Loose curls need less heat energy (in particular a lower temperature and/or a shorter heating time) and tight curls need more heat energy (in particular a higher temperature and/or a longer heating time). Thus, the heating control is based on the curl size, with lower heating energy (lower temperature and/or shorter heating time) for large curls than for small curls.

The heating temperature may not be constant over time. In such a case, the heating temperature may be taken to be the average heating temperature over the heating time period.

The controller may control the heater such that only the heating temperature is inversely correlated with the size of the barrel but with a fixed heating time. Thus, a temperature control loop may be used to control the heater. Each heating barrel size may then have an associated temperature setting.

Instead, the controller may control the heater such that only a heating time is inversely correlated with the size of the barrel with a fixed heating temperature. Each heating barrel size may then have an associated heating duration.

The two control approaches may be combined, so that each heating barrel size may be associated with a particular combination of heating temperature and heating time, for each curling operation. Between each barrel size there may be a change in one or both of the heating temperature and the heating time.

For example, a smallest barrel size, e.g., 25mm diameter, may be associated with a temperature of 200 degrees Celsius and a time of 10 seconds. A middle barrel size, e.g., 30mm diameter, may be associated with a temperature of 190 degrees Celsius and a time of 8 seconds. A largest barrel size, e.g., 35mm diameter, may be associated with a temperature of 170 degrees Celsius and a time of 8 seconds.

In order to control the heating conditions based on the heating barrel size, the heating barrel size needs to be known. There are various ways in which this is possible.

In one example, the adjustment of the heating barrel size may be achieved using an electrical actuator (e.g., motor). In this case, there is an electrical user interface for receiving the user input and generating a control signal to control the electrical actuator (motor). In such a case, an electrical signal already exists which represents the heating barrel size. This signal can thus be provided to the controller to enable the hair curler parameters to be controlled such as the heating time and/or temperature. Thus, a motor control signal can also be used by the controller as the heating control signal.

If there is no suitable electrical signal which represents the selected size of the heating barrel, a sensor may be used for this purpose. The sensor may be provided at any suitable location and it may be associated with any component which has a configuration which can be sensed and which represents the heating barrel size setting. For example, between the user interface (e.g., control knob, slider, switch) and the physical mechanism that adjusts the heating barrel size, there will be a drive chain. This drive chain may include mechanical and/or electrical or even hydraulic components. Any suitable component along the drive chain may be associated with a sensor, such as a position sensor or an electrical signal sensor, for detecting the size setting of the heating barrel. For example, the drive chain may include gears, and a gear position may be representative of the heating barrel size setting and may be sensed.

Another aspect of this disclosure relates to a particular design in which the barrel size changing mechanism is a manually-operated selector (with a plurality of operative positions and each different size associated with one of the operative positions of the manually-operated selector). The manually-operated selector operates a mechanical structure for changing the barrel size, by a mechanical coupling. Thus, the barrel size is adjusted by a purely mechanical mechanism, which is actuated by the physical configuration of the selector. This presents a problem that the mechanical system does not provide any electrical sensing signal.

This aspect of the disclosure thus provides a sensor which is coupled with the manually-operated selector for sensing the position of the manually-operated selector and providing a signal indicating the operative position of the manually-operated selector to the controller. The sensing unit is associated with the manual selector to sense the configuration (e.g., linear or rotational position of a slider switch or a rotatable knob or a push-button) of the operation unit instead of sensing the actual change of the barrel size.

Figure 4 shows a first implementation of the sensor according to this aspect. It shows the manually-operated selector in the form of a slider knob 60. The slider knob 60 is coupled to a sensing unit for sensing the position of the slider knob and generating a sensing signal indicating the operative position of the slider knob. In this example, the sensing unit is a magnetic sensor, and it comprises a first portion 62 in a fixed position relative to a body of the hair curler and a second portion 64 movable with the slider knob. In this way, a different magnetic coupling between the first and second portions 62, 64 is made in each operative position. Thus, the sensed type of magnetic coupling is indicative of the operative position of the selector, and the nature of the magnetic coupling may be considered to be a characteristic feature of the operative position.

In the example of Figure 4, the first portion 62 comprises a Hall sensor mounted on Hall sensor PCB 63 and the second portion 64 comprises a permanent magnet. Thus, the slider knob carries a permanent magnet and the static body of the curler carries a Hall sensor. More generally, one of the first and second portions comprises a detectable magnetic element and the other of the first and second portions is a magnetic sensor.

For an example with three size settings, there are three positions of the Hall sensor relative to the permanent magnet. The central position is shown, and the others are shown dotted in Figure 4. The Hall sensor is in this example placed in the middle of the sliding path (and it may be placed in the middle of a rotating path for a rotary control knob).

The positions of the magnetic element and the Hall sensor are of course interchangeable. Thus, the magnetic sensor can instead be be fixed to the user-controlled moving part of the selector (sliding button or rotary knob), and the magnetic element could be static and fixed at a position along the path of the selector (the rotating path of a rotary knob or a linear path of a sliding button).

Figure 5 shows the slider knob 60 mounted over the Hall sensor PCB 63 and the Hall sensor 62. The arrow 70 shows the permanent magnet and slider knob movement direction. Figure 5 schematically shows three possible sensor signals being provided to the controller 30, mounted on a controller PCB 31.

Figure 6 shows a second implementation of the sensor. In this example, the manually-operated selector is in the form of a rotary knob 80 which pivots (as shown by arrow 82) about a pivot axis 84. Near the pivot axis, the rotary knob 80 is coupled to an array of alternating (N-S-N-S) magnetic poles 86 which alternate along a direction of the rotary knob. These alternating poles form an annular magnet. The magnetic poles thus form the second (movable) portion of the magnetic sensor.

A Hall sensor 88 is mounted statically at the rotation axis on a Hall sensor PCB 90. The Hall sensor thus form the first (static) portion of the magnetic sensor.

The Hall sensor is in this example implemented as a magnetic encoder for sensing rotational position information, and the magnetic element and the magnetic encoder are placed at the pivot position of the rotary knob, and the magnetic element and the magnetic encoder are relatively rotatable. Instead of a magnetic sensor, another option is to use electrical contacts.

Figure 7 shows an example of the sensing unit which comprises a first set 102 of electrical contacts 102a, 102b, 102c in a fixed position relative to a body of the hair curler and a second set of electrical contacts 106 movable with the manually-operated selector 60. In this example, the first set comprises a set of three contacts 102a, 102b, 102c whereas the second set comprises a single contact 106. A characteristic electrical connection is made between one of the contacts of the first set and the single contact of the second set in each operative position.

The electrical contacts 102a, 102b, 102c of the first set are attached to a PCB 100 and the electrical contact 106 of the second set is attached to a PCB 104.

The electrical contacts are for example spring elements formed of an electrically conductive material. Each possible pair of connected spring elements correspond to a different signal to be generated for the heating system. The spring contacts may take any suitable form and any desired number of different positions can be implemented.

The changed electrical connection path results in a suitable signal to the controller 30 as shown in Figure 8. In this way, the signal is generated directly from the user when they operate the manually-operated selector. After receiving the signal, the processor 30 processes the signal and provides feedback to the heating system.

In the examples above, the barrel heating temperature and/or heating duration is controlled depending on the heating barrel size setting. However, in other examples, other parameters may be controlled as well or instead, such as the rotary drive of the looper.

Figure 9 shows a method of controlling the hair curler described above.

In step 110, the set size of the heating barrel is sensed so that a signal is generated indicating the operative position of the manually-operated selector.

In step 1112, an operation parameter of the hair curler is set based on the signal generated by the sensing unit.

According to one aspect of the invention, the heating barrel size is sensed using a sensor which senses the setting of a manually-operated selector, which is mechanically coupled to a barrel size changing mechanism.

According to another aspect of the invention, the operation parameter is the heating temperature and/or heating duration of the heating barrel, wherein one or both is inversely correlated with the size of the barrel.

The selector is explained above as being able to “move” or be “movable”. In the context of this invention, this may indicate movement along a linear path, or a curved path, it may also mean a rotation about an axis. In the case of a Hall sensor being implemented as a magnetic encoder, the relative movement between the magnetic element and the magnetic sensor is a rotation.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Functions implemented by a processor or controller may be implemented by a single processor or by multiple separate processing units which may together be considered to constitute a "processor". Such processing units may in some cases be remote from each other and communicate with each other in a wired or wireless manner.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

If the term "adapted to" is used in the claims or description, it is noted the term "adapted to" is intended to be equivalent to the term "configured to". If the term

"arrangement" is used in the claims or description, it is noted the term "arrangement" is intended to be equivalent to the term "system", and vice versa.

Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A hair curler (10), comprising: a heating barrel (18) around which hair is to be wound for curling and comprising a heater; a barrel size changing mechanism (40,42) adapted to change the size of the heating barrel in response to user input; and a controller (30) adapted to control the heater in dependence on the selected size of the heating barrel, such that a heating temperature and/or a heating duration applied to hair wound around the heating barrel (18) is inversely correlated with the size of the barrel.

2. The hair curler of claim 1, wherein the controller (30) is adapted to control the heater such that a heating temperature is inversely correlated with the size of the barrel.

3. The hair curler of claim 2, wherein the hair curler comprises a plurality of selectable heating barrel sizes, each having an associated temperature setting.

4. The hair curler of any one of claims 1 to 3, wherein the controller (30) is adapted to control the heater such that a heating time is inversely correlated with the size of the barrel.

5. The hair curler of claim 4, wherein the hair curler comprises a plurality of selectable heating barrel sizes, each having an associated heating duration.

6. The hair curler of any one of claims 1 to 5, comprising: a sensor (62,64; 86,88; 102,106) for sensing the selected size of the heating barrel for providing selected size information to the controller.

7. The hair curler of claim 6, comprising a selector (60) at which user input is received for changing the heating barrel size, wherein the sensor (62,64; 86,88; 102,106) is located at a location along a drive chain between the user operation unit and the heating barrel (18).

8. The hair curler of claim 6 or 7, wherein the barrel size changing mechanism (40, 42) comprises a manually-operated selector (60) which has a plurality of operative positions, such that the heating barrel can be driven to different sizes using the manually- operated selector in response to the user input, each different size associated with one of the operative positions of the manually-operated selector, wherein the sensor (62,64; 86,88; 102,106) is coupled with the manually- operated selector for sensing the position of the manually-operated selector and providing a signal indicating the operative position of the manually-operated selector to the controller (30).

9. The hair curler of claim 8, wherein the manually-operated selector (60) comprises a slider switch or a rotatable knob or a push-button.

10. The hair curler of any one of claims 1 to 5, comprising: an electrical user interface for receiving the user input and generating a control signal; and an electrical actuator for controlling the barrel size changing mechanism in response to the control signal, wherein the control signal is provided to the controller for controlling the heater.

11. The hair curler of any one of claims 1 to 10, wherein the heating barrel comprises a plurality of segments (50,52,54) which are configurable to form a shape of different size depending on the user input.

12. A method of controlling a hair curler, the hair curler comprising a heating barrel around which hair is to be wound for curling and comprising a heater and a barrel size changing mechanism adapted to change the size of the heating barrel in response to user input, wherein the method comprises: controlling the heater in dependence on the selected size of the heating barrel, such that a heating temperature and/or a heating duration applied to hair wound around the heating barrel is inversely correlated with the size of the barrel.

13. The method of claim 12, comprising controlling the heater such that a heating temperature is inversely correlated with the size of the barrel.

14. The method of claim 12 or 13, comprising controlling the heater such that a heating time is inversely correlated with the size of the barrel.

15. A computer program comprising computer program code which is adapted, when said program is run on a computer, to implement the method of any one of claims 12 to claim 14.