Electrical appliance with safety system

Abstract

An electrical appliance 2 comprising a main body having an electrical load component 6 and a safety monitor circuit 20 configured to output a safety signal based on at least one monitored operating pa

Description

B ACKGROUND A typical household will usually make use of appliances that include electrical heaters, such as personal grooming devices like hair dryers, hair straighteners, but also space heaters. Such appliances are governed by safety standards which dictate how such appliances should operate in the event of a fault. Examples of such standards are IEC / EN / UL 60335 and 60730. Since these types of appliances can draw relatively high current loads, they incorporate safety protection functions to ensure that electrical power is disabled in the event of an identified safety fault. It is known for these protection functions to be embodied by thermal fuses which are operable to disable the appliance when its operational temperature surpasses a safety threshold. It is against this background that the embodiments of the invention have been devised. SUMMARY According to an example of the invention, there is provided an electrical appliance, comprising a main body having an electrical load component and a safety monitor circuit configured to output a safety signal based on at least one monitored operating parameter of the electrical load component, the safety signal being indicative of a safe condition or an unsafe condition; wherein the safety signal is an optical signal, and a power supply module that is connected to the main body and configured to supply power thereto. The main body and the power supply module are connected to one another at a rotary interface comprising an electrical slip ring and an optical rotary joint, wherein the electrical slip ring is configured to convey at least electrical power from the power supply module to the main body, and wherein the optical rotary joint is configured to convey the safety signal from the main body to the power supply module. The power supply module comprises a power cut-out circuit adapted to receive the safety signal via the optical rotary joint and, in response, to interrupt electrical power to the electrical load component of the main body when the safety signal indicates an unsafe condition. An advantage of the invention is that the transmission of the safety signal of the electrical appliance is less susceptible to electromagnetic interference and so the power cut-out functionality of the appliance is more reliable because it is embodied as an optical solution. Furthermore, the electronic circuitry to receive and process the optical safety signal is less complex than would be the case with an electrical signal transmitted via slip rings as there is a lower need for fault tolerancing. Therefore, a less complex circuitry benefit is achieved which therefore brings reliability and cost benefits. In one example, the power supply module is connected to the main body by a power cable. This provides flexibility in how the main body is manipulated by a user, which is particularly useful in the context to the electrical load component being an electrical heater device for example as would be found in a hair styling appliance such as a hair dryer or a hair iron / tong for curling or straightening hair. The rotary interface in some examples is provided at the main body. Therefore, where the power supply module is part of an electrical cable, that electrical cable is able to rotate with respect to the main body. In some other embodiments, the rotary interface may be provided on the power supply module, or possible at an intermediate position along a power cable of the device. The power cut-out circuit may include a charge pump device which is configured to be energised by the safety signal indicating a safe condition and outputs a driving signal to a power relay. Accordingly, the charge pump device may be configured to be deenergised by the safety signal indicating an unsafe condition and terminates the driving signal to the power relay. Upon termination of the driving signal, the power relay cuts power to the main body. The charge pump device may be coupled to a semiconductor switch device which provides the driving signal to the power relay. The safety signal indicating a safe condition may comprise a pulsed optical signal that is input into the power cut-out circuit and is converted into an electrical signal for energising the charge pump device. In some examples, a second charge pump device to provide a redundant driving signal to the power relay. The optical emitter may be optically coupled to the optical rotary joint by a light guide. Similarly, the power cut-out circuit may be optically coupled to the rotary joint by an optic fibre. Where the rotary joint comprises an optical core, then the optical core may includes an input core component coupling the optical core to the light guide and / or an output core component coupling the optical core to the optic fibre. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of an electrical appliance in accordance with an example of the invention; Figure 2 is a more detailed schematic diagram of aspects of the electrical appliance of Figure 1, with an emphasis of a safety system of the appliance; Figure 3 is a more detailed illustration of circuit aspects of the safety system. DETAILED DESCRIPTION The examples of the invention relate generally to an architecture for a safety system in an electrical appliance which provides that appliance with suitable safety functionality. In the examples that are discussed below, and illustrated in the accompanying figures, the safety system provides control over the power that is supplied to a functional component of the electrical appliance. That component may be a lamp, motor or a heating device, for example, although these are just indicative of the types of components that are relevant to this discussion. By controlling the power supplied to the component, it can be disabled in circumstances where it is unsafe for the component to carry on functioning. Types of appliance that are applicable to the examples of the invention particularly include handheld hair styling appliances such as hair dryers, hair irons and curling tongs. Figure 1 provides a general overview in schematic form of an electrical appliance 2 according to an example of the invention, including an associated safety system 4. The electrical appliance 2 includes at least one functional component 6 which provides the appliance with suitable functionality. As mentioned, the component 6 can be considered to be a heater device, although either term may be used interchangeably. Such a heater device may be a wire-element type heater device such as found in typical hair dryers or a ceramicelement type heating device which are commonly found in hair straighteners and hair curling tongs, for example, but also in hair dryers produced by the Applicant. The electrical appliance 2 includes a power system 8 that provides power to the component 6. As shown, the power system 8 comprises a power plug 10 and a relay module 12. The power plug 10 is connected to the relay module 12 and in turn the relay module 12 is connected to the component 6 to supply power to it. The connections between the power plug 10, the relay module 12 and the component 6 may be achieved by way of a flexible electrical cable. Operation of the component 6 is controlled by a control system 14. The control system 14 is responsible for the general operation of the component 6. In the case of the component 6 being a heater device, the control system 14 may be responsible for turning the component 6 on and off under the command of a user interface 16, that provides an array of interactive controls to allow the user to regulate the operating temperature of the device and so on. The user interface 16 may be embodied by any suitable user-operable controls for example push buttons, sliding toggle switches, touch screens or it may feature voice-operated commands. The precise configuration of the control system 14 and the user interface 16 is not central to the invention and so further discussion will be omitted for the sake of clarity. The safety system 4 operates whilst the heater device 6 is being controlled by the control system 14 and provides a supervisory control function which can override the functionality of the control system 14 in circumstances where the safety system 4 detects that the heater device 6 is in an unsafe condition. In overview, and with initial reference to Figure 1, the safety system 4 comprises a sensing module 18, a safety processor module 20, and a power cut-out module 22. The power cutout module 22 is interfaced with the relay module 12 which also therefore forms part of the safety system 4. Notably, and as will be discussed in further detail later, the electrical appliance includes a main body assembly 23a and a cable assembly 23b. The cable assembly 23b includes a box or housing 25 which contains the power cut-out module 22 and relay module 12. In an alternative example, the power plug may be contained within the housing 25. The connection between the main body assembly 23a and the cable assembly 23b for the purposes of transmitting electrical power and communication signals is achieved by way of a hybrid interface 30 which incorporates functionality for transferring electrical signals as well as optical signals. Further details of the hybrid interface 30 are provided in the following discussion. As will become clear, the function of the safety processor module 20 is to monitor the operation of the heater device 6, using the sensor module 18, and detect when an unsafe condition exists. In response to the detection of an unsafe condition, the safety processor module 20 is operable to control the relay module 12 in order to interrupt power supply to the heater device 6. The different functional modules of the electrical appliance 2 will now be described in more detail, with reference also to Figure 2. The sensing module 18 in this example of the invention comprises a plurality of sensing elements, although the individual elements are not shown here. As mentioned, the component 6 in this example is a heating device and so the sensing elements may be suitably arranged in and around the heating device to provide a reliable means of detecting an unsafe temperature condition. It is envisaged that in a wire-type heating element, the sensing elements could be placed next to the wire heating elements in order to measure accurately the temperature of the air near to the heating elements. Similarly, in the case of a heating element comprising a ceramic block, the sensing elements may be fully or partially embedded within the body of the ceramic material. It is currently considered useful to provide several sensing elements to have the capability to measure the temperature of the heating device in many different places which generally is a more reliable way to carry out that function. However, a single sensing element may also be acceptable in some applications. The term ‘sensing module’ therefore refers to one or more sensing elements, whether then are combined together in some way or distributed about the heating device or elsewhere in the electrical appliance 2. The sensing module 18 is connected to the safety processor module 20 by a suitable connector 24. In this example, a sensor interface 26 is disposed between the connector 24 and the safety processor module 20 to carry out appropriate signal conditioning on the raw sensing signals being received by the individual sensing elements of the sensor module 18. The required functionality of the sensor interface 26 is conventional and would be well understood by the skilled person and so a detailed explanation will not be provided here. In summary, however, the sensor interface 26 receives the raw signals from the individual sensing elements and conditions these into a suitable format as appropriate for the safety processor module 20. As shown in Figure 2, the sensor interface 26 and the safety processor module 20 interact through a plausibility checking protocol, shown here generally as ‘27’, as would be understood by the skilled person as a known technique that enables the safety processor module 20 to inject known values into the data stream from the sensor interface 26 in order to check that valid data is being converted correctly from analogue to digital format thereby providing a means to detect certain component faults. As will be discussed further later, the safety processor module 20 outputs a pulsed activation signal 29 for as long as it determines that the component 6 is in a safe state. The activation signal 29 is conveyed from the body assembly 23a to the cable assembly 23b by way of the hybrid interface 30, as mentioned briefly above. The hybrid interface 30 in this example is a hybrid rotary interface and serves to convey power to the main body assembly 23a by a set of electrical slip rings 32. In this example, the set of electrical slip rings 32 includes a first slip ring 34 which is associated with a live power line 36, and a second slip ring 37 which is associated with a neutral power line 38. The live and neutral power lines 36,38 extend from the power plug 10. The hybrid interface 30 also includes an optical rotary joint 40 comprising an optical core 42. The optical core 42 is sometimes known in the art as an optical slip ring. It should be noted that hybrid rotary interfaces combining the transmission of electrical power and / or data signals and also optical data signals are known in the art and are available commercially. Therefore, a detailed technical discussion of this component will not be provided here. The activation signal 29 is input to an optical emitter module 44 which converts the signal into a form that is suitable for onward transmission along a fibre optic element 31 of the cable assembly 23b. The optical emitter module 44 provides an input to the optical core 42. It should be noted that the safety processor module 20 and the optical emitter module 44 are shown as separate modules or parts in this discussion, for convenience, but this separation is not essential. The safety processor module 20 and the optical emitter module 44 together form a safety monitor circuit that is operable to sense an unsafe condition and output an optical safety signal. The optical input from the optical emitter 44 to the optical core 42 may be provided by a suitable light guide 43. The light guide 43 may be a suitable light conveyance device for example of glass or plastic that is rigid and fixed within the main body to convey optical data from the optical emitter 44 to the optical core 42. The light guide 43 and optical rotary joint 40 are not in contact and an air gap is formed between the light guide 43 and optical rotary joint 40. As long as the light guide 43 is axially aligned with the optical rotary joint 40, optical data can be conveyed from the optical emitter 44 to the optical core 42. In one embodiment, the safety signal from the main body assembly can be transmitted to the cable assembly via the optical data carried via the light guide 43 in the main body assembly and the optical fibre through the centre of the electrical slip rings 32 and to the cable assembly. In this embodiment, the optical rotary joint 40 may be a rotary or nonrotary joint at the centre of the hybrid interface 30. Specifically, the optical rotary joint 40 is at the centre of the electrical slip rings 32 and the optical data can be conveyed from the optical emitter 44 to the optical core 42 through the air gap In this manner, the optical emitter 44 in the moving part of the main body assembly can transmit the optical data through the air gap into the fibre optical element 31 held in the centre of the electrical slip rings 32 and carried down the interconnecting cable assembly. In turn, the optical core 42 provides a rotary coupling to the fibre optical element 31 of the cable assembly. As such, the cable assembly 23b and the main body assembly 23 are able to rotate with respect to one another whilst still transmitting data between them. The optical core may comprise an input core component and an output core component. The input core component and the output core component may be arranged to rotate relative to one another. The rotation may be about a common aligned axis. The input core component may be coupled to the light guide 43 by an input collimator for the transition of optical power. Likewise, the output core component may be coupled to the optical fibre 31 by an output collimator. The optical fibre and the light guide 43 may be aligned on the common axis. At this point it should be noted that the optical fibre may be integral with the optical core 42, that is to say to pass through a component of the optical core 42. Alternatively, a separate optical transmission component, e.g. a separate light guide (not shown in Figure 2), may be provided to couple the optical signal from the input light guide 43 to the fibre optical element 31. In this example, the cable assembly 23b includes a single fibre optic element 31 although multiple fibre optic elements may be incorporated for the transmission of multiple signals. In this respect, the optical core 42 provides a single-mode optical coupling in this example, although in other examples the optical core 42 may be configured to provide a multi-core optical coupling to support multiple data signals along different fibre optic elements. As an alternative example, a single fibre optic element 31 may convey multiple optical signals by using multiple optical emitter / receiver pairs operating at different wavelengths of light. At this point it should be appreciated that for convenience the sensor interface 26, the safety processor module 20, and the optical emitter 44 may be embodied on a common circuit board, although this is not essential. As shown in the figures, the safety processor 20 is a dedicated hardware unit. However, it should be noted that the algorithms and routines run on the safety processor may also be run on a microprocessor that is responsible for operating other functions of the electrical appliance. The optical activation signal 29 is received from the fibre optic element 31 by an optical receiver module 46 of the power cut-out module 22. The optical receiver module 46 operates to convert the received optical signal to an electrical signal appropriate for input into to a charge pump circuit 48 of the power cut-out module 22. The charge pump circuit 48 includes a pair of charge pumps 50a,50b which are energised by the activation signal 29 and which in turn maintain the relay module 12 in an energised state, thereby permitting power to be supplied to the heater device 6. The charge pumps 50a,50b each receive an identical activation signal 29a,29b from the optical receiver module 46. The activation signals 29a,29b therefore provide a pulsating input voltage signal to the input terminal of the charge pumps 50a,50b, as driven by the safety processor module 20. In response to the input activation signals 29a,29b, the charge pumps 50a,50b output respective driving signals 52a,52b. Since the typical output voltage of a charge pump is relatively low, in this example the power cut-out module 22 includes respective semiconductor switches 54a,54b, which in this case are labelled as MOSFETs, although the skilled person would understand that other semiconductor switches would also be acceptable. As can be seen in Figure 2, each of the semiconductor switches 54a,54b is connected to a respective terminal of a relay coil 56 of the relay module 12 such that, when the semiconductor switches 54a,54b are turned on, the circuit of the relay coil 56 is maintained in an energised state, thereby maintaining an associated relay switch 58 in a closed state. Figure 3 shows a more detailed circuit topology of the charge pumps 50a,50b. As shown, the differential activation signal 29 is received by the optical receiver module 46, which outputs an identical activation signal 29a,29b to the charge pumps 50a,50b. Each of the charge pumps 50a,50b is identical in form in order to maintain the same functionality in response to the input charge pulse and, as is conventional, comprise a network of resistors, diodes and capacitors to achieve the voltage boosting functionality. Expressed another way, each of the charge pumps 50a,50b can be considered to be a form of voltage multiplier circuit or analogue monostable circuit in which its output is held high as long as oscillating charge pulses are present at the input. As shown in this example, each charge pump circuit comprises two cells each comprising capacitors 60 and a diode 62. The capacitors 60 and diodes 62 are switched by the pulsing input signal, which can be considered to be an alternating voltage input, and produce an output voltage across an output resistor 64 into the respective gates of the semiconductor switches 54a,54b. The alternating voltage input voltage effectively passes through the series capacitor and charges the output capacitor during each pulse, whereas the diodes help prevent reverse discharge and clamp the minimum voltage level of the output, as would be well understood by a skilled person. In the event that the alternating voltage input is removed, the output capacitor 60 will discharge through the resistor 64, thereby turning off the respective semiconductor switch 54a,54b. Figure 3 also shows a more detailed implementation of the first and second semiconductor switches 54a,54b in this example of the invention. As discussed above in relation to Figure 2, each of the semiconductor switches 54a, 54b is connected to a respective side of the relay coil 56 so that both semiconductor switches 54a,54b need to be turned on in order for the relay coil 56 to be energised and thereby operate the relay switch 58. More specifically, the high side of the relay coil 56 is connected to semiconductor switch 54a and the low side of the relay coil is connected to semiconductor switch 54b. Due to the specific component selection, in this example, the functionality of the first semiconductor switch 54a is formed by a combination of two components, here labelled as M2 and M3. As such, the component M2 inverts the output driving signal of the charge pump 50a in order to provide a voltage that is compatible with the PMOS type semiconductor component M3. Other techniques and topologies for switching the high and low sides of the relay coil 56 would be apparent to the skilled person and the above discussion should be considered as an example of one acceptable option. Beneficially, the safety system 4 provides failsafe functionality by virtue of the pulsed activation signal. As has been mentioned, the safety processor module 20 functions to provide a high frequency pulsed signal which is boosted by the charge pumps 50a,50b. As long as the pulsed activation signal 29 is output by the safety processor module 20, the charge pumps 50a,50b will supply a sufficient voltage, via the semiconductor switches 54a,54b, to the relay coil 56 so as to maintain it in an energised state. However, in the event the safety processor module 20 detects that the heating device 6 is at an unsafe temperature, it will terminate the output of the pulsed activation signal 29. When this happens, the signal 66a,66b (not labelled on Fig 3) provided to the semiconductor switches 54a,42b will decay and will after a given time period will fall below the voltage required to drive the semiconductor switches 54a,54b. At this point, the relay coil 56 will change to a deenergised state, thereby opening the relay switch 58 which will have the effect of terminating the power supply to the heater device 6. The power cut-out module 22 and the relay module 12 therefore operate together to provide a power cut-out functionality for the electrical appliance, and so together can be considered to be a power cut-out module. It should also be noted that a further benefit is provided by the activation signal 29 being conveyed from the body assembly 23a to the power cut-out module 22 by way of the hybrid interface 30. Firstly, the use of an optical signal path for the activation signal 29 means that the activation signal 29 is less susceptible to electromagnetic interference and therefore has a greater degree of fault tolerance. The electronic complexity required by the power cut-out module 22 is therefore reduced compared to an approach using conventional resistive wires. What is more, since the interface combines electrical and optical transmission systems, the electrical complexity of the rotary joint is reduced by the reduction in number of electrical slip rings. It should also be appreciated that the charge pump circuitry is housed in the cable assembly 23b, and so is physically separated from the main body assembly 23a of the electrical appliance. This arrangement is beneficial because it helps to avoid an increase in the packaging size of the main body assembly to house the components associated with the charge pump circuity. Product downsizing is an important consideration in the design of personal grooming products particularly, and this conflicts against the requirement to incorporate sophisticated failsafe circuitry. Therefore, locating the charge pump circuitry in a separate housing on the cable assembly together with the relay coil 56 and relay switch 58 is a particularly elegant arrangement. The illustrated examples of the invention show one way in which the invention may be implemented. Some alternatives have been mentioned above, and the skilled person would understand that other variations may be made to the illustrated examples without departing from the invention as defined by the claims. For example, in the above discussion, the hybrid interface 30 is provided by a hybrid rotary joint that supports the transmission of electrical power as well as one or more optical data signal signals. This is beneficial in the case of an electrical appliance with a rotatable connection between a main body and a power cable and some advantages of this configuration have been discussed above in connection with the transmission of a safety signal that is transmitted between the main body assembly 23a and a power cut-out module 22 housed within the cable assembly 23b, for example in a power plug or a cable box. However, the same or similar advantages apply to configurations where the hybrid interface is not a rotatable interface and also where the data signals sent through the optical 5 interface are not related to the electrical safety of the appliance. For example, other types of optical data may relate to the power (for example voltage level and frequency) that the electrical appliance receives from a mains power socket such that the control system within the main body 23a may configure power-consuming components correctly. This could be an advantage where the electrical appliance is expected to be used in countries which make 10 use of different mains power supplied (e.g. 240 50Hz, versus 110V 60Hz).

Claims

1. An electrical appliance, comprising:a main body having an electrical load component and a safety monitor circuit configured to output a safety signal based on at least one monitored operating parameter of the electrical load component, the safety signal being indicative of a safe condition or an unsafe condition; wherein the safety signal is an optical signal;a power supply module that is connected to the main body and configured to supply power thereto,wherein the main body and the power supply module are connected to one another at a rotary interface comprising an electrical slip ring and an optical rotary joint; wherein the electrical slip ring is configured to convey at least electrical power from the power supply module to the main body, and wherein the optical rotary joint is configured to convey the safety signal from the main body to the power supply module;wherein the power supply module comprises a power cut-out circuit adapted to receive the safety signal via the optical rotary joint and, in response, to interrupt electrical power to the electrical load component of the main body when the safety signal indicates an unsafe condition.

2. The electrical appliance of Claim 1, wherein the power supply module is connected to the main body by a power cable.

3. The electrical appliance of Claim 1 or 2, wherein the electrical load component includes an electrical heater device.

4. The electrical appliance of Claim 3, wherein the electrical appliance is a hair styling device.

5. The electrical appliance of Claim 4, wherein the hair styling device is a hair dryer.

6. The electrical appliance of Claim 4, wherein the hair styling device is a hair iron forcurling or straightening hair.

7. The electrical appliance of any one of the preceding claims, wherein the rotary interface is provided at the main body.

8. The electrical appliance of any one of the preceding claims, wherein the power cutout circuit includes a charge pump device which is configured to be energised by the safety signal indicating a safe condition and outputs a driving signal to a power relay; and wherein the charge pump device is configured to be deenergised by the safety signal indicating an unsafe condition and terminates the driving signal to the power relay;wherein when the power relay is configured to cut power to the main body upon termination of the driving signal.

9. The electrical appliance of Claim 8, wherein the charge pump device is coupled to a semiconductor switch device which provides the driving signal to the power relay.

10. The electrical appliance of Claim 8 or Claim 9, wherein the safety signal indicating a safe condition comprises a pulsed optical signal that is input into the power cut-out circuit and is converted into an electrical signal for energising the charge pump device.

11. The electrical appliance of any one of the preceding claims, wherein the power cutout circuit includes a second charge pump device to provide a redundant driving signal to the power relay.

12. The electrical appliance of any one of the preceding claims, wherein the optical rotary joint includes an optical emitter.

13. The electrical appliance of Claim 12, wherein the optical emitter is optically coupled to the optical rotary joint by a light guide.

14. The electrical appliance of any one of the preceding claims, wherein the power cutout circuit is optically coupled to the rotary joint by an optic fibre.

15. The electrical appliance of any one of the preceding claims, wherein the rotary joint comprises an optical core.

16. The electrical appliance of Claim 15, when dependent on Claim 13, wherein the optical core includes an input core component coupling the optical core to the light guide.

17. The electrical appliance of Claim 15, when dependent on Claim 14, wherein the optical core includes an output core component coupling the optical core to the optic fibre.

18. The electrical appliance of claim 15, when dependent on Claim 13, wherein the rotary joint is arranged at the centre of the electrical slip ring and an air gap is defined between the rotary joint and the light guide.

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