WO2022123201A1

WO2022123201A1 - Electrical appliance with safety system

Info

Publication number: WO2022123201A1
Application number: PCT/GB2021/052941
Authority: WO
Inventors: Kishan AMRATIA
Original assignee: Dyson Technology Limited
Priority date: 2020-12-09
Filing date: 2021-11-15
Publication date: 2022-06-16
Also published as: GB202019397D0; CN116548066A; GB2601771A

Abstract

An electrical appliance comprising: a main body assembly which includes a processing module configured to detect a safety condition for the electrical appliance; and a power cable assembly which includes a includes a power cut-out module. The processing module is configured to transmit an activation signal to the power cut-out module which indicates a safe condition or an unsafe condition for the electrical appliance, and wherein the power cut-out module is configured to terminate power supply to the main body assembly when the activation signal indicates an unsafe condition.

Description

ELECTRICAL APPLIANCE WITH SAFETY SYSTEM

FIELD OF THE INVENTION

The invention relates generally to an electrical appliance such as a hairdryer or space heater having a safety system configured to disable power supply to the appliance when an unsafe condition is detected.

BACKGROUND

Electrical appliances that incorporate electrical heaters are common about the average home and may include personal grooming devices such as hair dryers, hair straighteners, but also space heaters. In order to make such appliances safe to use, household electrical 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.

A typical requirement is for appliances to incorporate protection control functionality to ensure that electrical power to the appliance is disabled in the event of a safety fault being identified. Moreover, the disabling of the power supply should be nonresettable control such that the user of the device is not able to reset the appliance in order to restore operation.

In an appliance that incorporates an electrical heater, typically such a non-resettable safety function is provided by a thermal cut-off that makes use of a thermal fuse which is operable to disable the appliance when its operational temperature reaches an unsafe level. Examples of such electrical appliances that could incorporate such safety functionality are described in W02015/005024 A1 and WO2018/130832 A1.

One design challenge associated with these electrical appliances is to make them more ergonomic by reducing their weight and size so that they are more easily held and operated by the user. This compromises the ability to design their electrical control systems to incorporate additional safety devices such as thermal fuses in reduced packaging volume. As alternative approach is therefore desirable which provides the same safety functionality that meets the relevant safety standard requirements but in a smaller package. It is against this background that the embodiments of the invention have been devised.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided an electrical appliance including a safety system, comprising a sensing module for sensing at least one operating parameter of the electrical appliance, a processing module interfaced to the sensing module which is configured to output an activation signal indicating a safe condition or an unsafe condition for the electrical appliance, a driver module which is configured to receive the activation signal from the processing module and output a driving signal, a relay module configured to receive the driving signal, wherein the relay module is configured to control a power supply to an electrical load of the appliance. The driver module includes a charge pump device, which is energised by the activation signal indicating a safe condition, and wherein when the activation signal indicates an unsafe condition, the charge pump device terminates the driving signal to the relay module which cuts out power supply to the electrical load.

Advantageously, the invention provides an electrical appliance having a safety system which is implemented in an elegantly simple manner and which trips into a safe condition if a problem manifests in the safety processor.

The charge pump device may be coupled to a semiconductor switch device which provides the driving signal to the relay module. Beneficially, therefore, the semiconductor switch device provides flexibility in the voltage supply that energises or deenergises the relay module.

The driver module may include a second charge pump device to provide a redundant driving signal to the relay module. Such a configuration provides redundancy benefit because the failure of one ‘leg’ of the charge pump means that the relay module will be deenergised.

The activation signal indicating a safe condition may comprise a pulsed signal that is input into and thereby energises the charge pump device. Beneficially, the electrical appliance may be configured to physically separate components of the safety system from the main body of the electrical appliance. Therefore, in one example, the processing module is contained within a main body assembly of the electrical appliance whereas the driver module and or the relay module may be contained within a power cable assembly of the electrical appliance. This configuration enables components of the safety system to be located away from the main body of the appliance which means that the main body can be designed to be a smaller package size since it is not required to house additional electrical components such as circuit boards and relay switches that are associated with the safety system.

The electrical load of the electrical appliance may be an electric heater device, by way of example, although other loads such as motors are also envisaged and therefore encompassed by the invention.

The sensing module may include a single sensing element, but also may include a plurality of sensing elements in order to enable a greater area of the electrical appliance to be monitored

In accordance with a second aspect, there is provided an electrical appliance comprising: a main body assembly which includes a processing module configured to detect a safety condition for the electrical appliance; and a power cable assembly which includes a includes a power cut-out module. The processing module is configured to transmit an activation signal to the power cut-out module which indicates a safe condition or an unsafe condition for the electrical appliance, and wherein the power cut-out module is configured to terminate power supply to the main body assembly when the activation signal indicates an unsafe condition.

Separating components of the safety system from the main body of the electrical appliance into the power cable assembly means that it is possible to downsize the main body as it does not have to house sizable components such as circuit boards and relay modules associated with the safety system. As well as a reduced packaging size, such a configuration also realises a lighter weight product which is a benefit particularly for handheld electrical appliances. The power cut-out module may include a charge pump device which receives the activation signal and, in response to the identification of an unsafe condition, triggers the termination of the power supply to the main body assembly. Using a charge pump device in this way provides a particularly elegant implementation to cutting out the power following the identification of a hazardous condition such as a device overtemperature. The charge pump device may be interfaced to a relay module and may be configured to disable the relay module when the activation signal indicates an unsafe condition for the electrical appliance.

Rather than directly driving the relay module the charge pump device may be coupled to a semiconductor switch device which provides a driving signal to the relay module. A further charge pump device may be provided to control the operation of the relay module which provides redundancy into the system.

The power cut out module may include the relay module contained within the power cable assembly of the electrical appliance.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

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; and

Figure 4 is a timing diagram that illustrates the operation of the safety system.

In the drawings, the same reference numerals are used to denote features that are common across drawings.

SPECIFIC 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 component 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.

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 4 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 ceramic-element 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 at least in part by way of a flexible electrical cable. However, it may also be the case that the relay module 12 and the power plug 10 are integrated into a common unit.

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 driver module 22. The driver 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 driver module 22 and relay module 12.

As will become clear in the discussion that follows, 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 particular 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 so as 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 so as 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 in order 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 shown here as a differential signal, as is well known in the art, which provides improves resistance to electromagnetic interference. The activation signal 29 is input to a signal output block 30 which converts the signal into a form that is suitable for onward transmission along a connection cable 31 . The connection cable 31 in this example comprises a complimentary pair of wires, as is known in the art and as is consistent with the differential nature of the activation signal 29. At this point it should be appreciated that for convenience the sensor interface 26, the safety processor module 20, and the signal output block 30 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 activation signal 29 is received by a signal conditioning circuit 32 of the relay driver module 22. The signal conditioning circuit 32 operates to suppress noise on the activation signal 29 and boost the signal as appropriate for input into to a charge pump circuit 34 of the relay driver module 22.

The charge pump circuit 34 includes a pair of charge pumps 36a, 36b 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 36a, 36b each receive an identical activation signal 29a, 29b from the signal conditioning circuit 32. The activation signals 29a, 29b therefore provide a pulsating input voltage signal to the input terminal of the charge pumps 36a, 36b, as driven by the safety processor module 20. In response to the input activation signals 29a, 29b, the charge pumps 36a, 36b output respective driving signals 40a, 40b. Since the typical output voltage of a charge pump is relatively low, in this example the relay driver module 22 includes respective semiconductor switches 42a, 42b, 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 42a, 42b is connected to a respective terminal of a relay coil 44 of the relay module 12 such that, when the semiconductor switches 42a, 42b are turned on, the circuit of the relay coil 44 is maintained in an energised state, thereby maintaining an associated relay switch 46 in a closed state.

Figure 3 shows a more detailed circuit topology of the charge pumps 36a, 36b. As shown, the differential activation signal 29 is received by the signal conditioning circuit 32, which outputs an identical activation signal 29a, 29b to the charge pumps 36a, 36b. Each of the charge pumps 36a, 36b 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 36a, 36b 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 a capacitor 50 and a diode 52. The capacitors 50 and diodes 52 are switched by the pulsing input signal, which can be considered to be an alternating voltage input, and produce a output voltage across an output resistor 54 into the respective gates of the semiconductor switches 42a, 42b. 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 will discharge through the resistor, thereby turning off the respective semiconductor switches.

Figure 3 also shows a more detailed implementation of the first and second semiconductor switches 42a, 42b in this example of the invention. As discussed above in relation to Figure 2, each of the semiconductor switches is connected to a respective side of the relay coil 44 so that moth semiconductor switches need to be turned on in order for the relay coil 44 to be energised and thereby operate the relay switch 46. More specifically, the high side of the relay coil is connected to semiconductor switch 42a and the low side of the relay coil is connected to semiconductor switch 42b. Due to the specific component selection, in this example, the first semiconductor switch 42a functionality 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 36a 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 44 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 36a, 36b. As long as the pulsed activation signal 29 is output by the safety processor module 20, the charge pumps 36a, 36b will supply a sufficient voltage, via the semiconductor switches 42a, 42b, to the relay coil 44 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 40a, 40b provided to the semiconductor switches 42a, 42b will decay and will after a given time period will fall below the voltage required to drive the semiconductor switches. At this point, the relay coil 44 will change to a deenergised state, thereby opening the relay switch 46 which will have the effect of terminating the power supply to the heater device 6. The driver 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 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 44 and relay switch 46 is a particularly elegant arrangement.

By way of further explanation of the functionality of the safety system 4, Figure 4 illustrates a series of timing diagrams or waveforms for various signals within the safety system 4. The waveforms are labelled 4(a) to 4(e) for clarity, with waveform 4(a) indicating the temperature profile of the heater device 6 over a time period, as measured by the sensor module 18; waveform 4(b) indicating the sampling frequency of the sensor module 18; waveform 4(c) indicating the pulsed activation signal 29 from the safety processor module 20; waveform 4(d) indicating the output voltage of the charge pumps 36a, 36b; and waveform 4(e) indicating the energisation state of the relay module 12.

As can be seen from waveform 4(a), starting from to the temperature of the heater device 6 is below a critical operating temperature threshold TOP but rises steadily and breaches the threshold TOP at time t1 .

During the time period to to t1 , it can be seen from waveform 4(b) that the sensed temperature is being acquired by the safety processor module 20 and the pulsed safety drive signal is being output by the safety processor module 20.

Once the temperature T exceeds the threshold TOP the safety processor module 20 implements a predetermined time period t_operating at the end of which it disables the activation signal 29. The time period t_operating is implemented in order to avoid spurious temperature spikes from triggering the system unnecessarily and may be set to any appropriate value. However, it should be noted that the delayed termination of the activation signal 29 as shown here is not essential. One option here is for the time period t_operating to be set as the reciprocal of the sampling frequency for the temperature signal. For example, if the sampling period is 100ms, then the time period t_operating will be 1 second. However, this is not essential and other setups are possible, as would be understood by the skilled person. By way of an example of such an alternative, the sampling interval may be 50ms, and the time period t_operating may be based on two successive readings being over-temperature.

As will be appreciated by waveform 4(c) and 4(d), the activation signal 29 that is output from the safety processor module 20 provides a charging pulse to the charge pump circuit 34 which requires charge pulses to keep its output voltage ‘topped up’. In the usual way, therefore, the charge pumps 36a, 36b boost the voltage level of the input activation signal 29 to a higher voltage, albeit temporarily, and provide a decaying output voltage that needs to be fed with a repeating input voltage pulse to maintain the output voltage at an acceptable level.

The end of the time period t_operating marks the end of the train of charge pulses, at time t2, at which point the charge pump circuit 34 stops receiving the input activation signal 29 and so the output voltage, which is input into the semiconductor switches, starts to decay. After a further time period, extending up to t4, which is governed by the specific electronic components that define the charge pumps 36a, 36b, the output voltage of the charge pumps decays past a voltage threshold V_SWitch which is required to maintain the semiconductor switches 42a, 42b in an operating condition. At t4, therefore, the semiconductor switches 42a, 42b turn off which de-energises the relay module 12, as can be seen by waveform 4(e). At this point, therefore, the power supply to the heater device 6 is disabled permanently and so the user of the electrical appliance is prevented from further using the appliance. The permanent removal of the power supply to the heater device may be achieved within the safety processor by the setting of an internal flag in its internal non-volatile memory which prevents the software routine from generating the pulsed activation signal even after a power cycle of the electrical appliance. Other means for disabling the activation signal would be apparent to the skilled person.

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.

Claims

1. An electrical appliance comprising: a main body assembly which includes a processing module configured to detect a safety condition for the electrical appliance; and a power cable assembly which includes a includes a power cut-out module; wherein the processing module is configured to transmit an activation signal to the power cut-out module which indicates a safe condition or an unsafe condition for the electrical appliance, and wherein the power cut-out module is configured to terminate power supply to the main body assembly when the activation signal indicates an unsafe condition.

2. The electrical appliance of Claim 1 , wherein the power cut-out module includes a charge pump device which receives the activation signal and, in response to the identification of an unsafe condition, triggers the termination of the power supply to the main body assembly.

3. The electrical appliance of Claim 2, wherein the charge pump device is interfaced to a relay module and is configured to disable the relay module when the activation signal indicates an unsafe condition for the electrical appliance.

4. The electrical appliance of Claim 3, wherein the charge pump device is coupled to a semiconductor switch device which provides a driving signal to the relay module.

5. The electrical appliance of Claims 3 or 4, wherein the relay module is contained within the power cable assembly of the electrical appliance.

6. The electrical appliance of Claim 2 to 5, including a second charge pump device.