Device with resistive heater and light sensor

Abstract

A device, such as a hair dryer or space heater, includes an air path comprising an inlet and an outlet. A resistive heating element is disposed in the air path for heating air passing through it. An airflow generator causes air to enter through the inlet, travel along the air path past the resistive heating element, and exit through the outlet. A light sensor is configured to receive light from the resistive heating element, the light sensor being configured to sense a wavelength range as an appropriate subset of the visible spectrum, at least a portion of the wavelength range including wavelengths indicative of overheating of the resistive heating element. The device is configured such that the light sensor sensing light within said wavelength range from the resistive heating element results in a reduction or isolation of power to the resistive heating element.

Description

Background Technology

[0001] A device is known that uses a resistance heating element to heat air passing through an air path. A driving current passes through the heating element, which heats the air and transfers the heat to the air passing through it in the air path. An impeller can be used to draw air through the air path. Examples of such devices include hair styling equipment, such as hair dryers and space heaters. Summary of the Invention

[0002] According to an embodiment of the present invention, an apparatus is provided, comprising:

[0003] Air path, which includes inlet and outlet;

[0004] A resistance heating element, which is placed in the air path, is used to heat the air passing through the air path;

[0005] An airflow generator is used to draw air in through an inlet, guide it along an air path past a resistance heating element, and exit through an outlet; and

[0006] A light sensor configured to receive light from a resistive heating element, the light sensor being configured to sense a wavelength range that is an appropriate subset of the visible spectrum, at least a portion of the wavelength range including wavelengths that indicate overheating of the resistive heating element;

[0007] The device is configured such that the light sensor senses light within the wavelength range from the resistive heating element, resulting in a reduction or isolation of power to the resistive heating element.

[0008] By sensing such a wavelength range, the device can quickly reduce or isolate the power to the resistance heating element in the event of overheating.

[0009] The device may include a controller coupled to receive an optical signal from a light sensor and to control a resistance heating element, the controller being configured to:

[0010] The optical sensor receives an optical signal that indicates the wavelength and / or intensity of the light generated by the resistive heating element.

[0011] The overheating of the resistance heating element is determined based on the wavelength and / or intensity indicated by the light signal; and

[0012] In response to determining that the resistance heating element is overheating, the power to the resistance heating element is reduced or the resistance heating element is isolated.

[0013] Regarding reducing the power supplied to the resistance heating element in the event of overheating, the use of a controller can provide increased flexibility and / or improved performance.

[0014] The device may also include a temperature sensor having a slower response time than a light sensor and being coupled to provide a temperature signal to a controller configured to:

[0015] A temperature signal is received from a temperature sensor, which indicates the temperature of at least a portion of the resistance heating element;

[0016] Based on the temperature signal, it is determined that the resistance heating element is overheating; and

[0017] In response to determining that the resistance heating element is overheating, the power supplied to the resistance heating element is reduced or isolated.

[0018] Using light and temperature sensors can improve the responsiveness to overheating modes of different types of resistance heating elements.

[0019] The controller can be configured to reduce or isolate the power to the resistance heating element in response to determining that at least a portion of the resistance heating element is overheating based on a light signal, regardless of whether the temperature signal indicates that the resistance heating element is overheating. This can help detect hot spots on the resistance heating element.

[0020] Optionally, when the controller reduces or isolates power to the resistance heating element in response to determining, based on the light signal, that at least a portion of the resistance heating element is overheating, the controller causes a stored indication that the resistance heating element has been reduced or isolated in response to the light signal. Storing the indication in this way can allow for improved troubleshooting and / or guidance regarding the maintenance and / or repair of the device.

[0021] Optionally, when the controller reduces or isolates the power to the resistance heating element in response to determining, based on the optical signal, that at least a portion of the resistance heating element is overheating, the controller may:

[0022] The device is put into a resistance heating element cleaning mode, in which the airflow generator controls the airflow through the air path in an attempt to remove any blockages that may have caused localized hot spots on the resistance heating element, resulting in a light signal indicating that the resistance heating element is overheating.

[0023] Output an instruction to the user that the device should be placed in the resistance heating element cleaning mode;

[0024] It outputs an indication to the user that the power to the resistance heating element is reduced or isolated in response to a light signal;

[0025] Output fault status indications to the user; and / or

[0026] It outputs instructions to the user that the device needs maintenance or repair.

[0027] Each of these options offers a different advantage in the event of overheating of the resistance heating element.

[0028] The wavelength range can have a lower cutoff wavelength of 550 nm. This excludes wavelengths that are unlikely to indicate overheating of the resistance heating element.

[0029] The wavelength range can have an upper cutoff wavelength of 780 nm. This excludes wavelengths that are unlikely to indicate overheating of the resistance heating element.

[0030] The detection peaks within the wavelength range can be concentrated between 550 nm and 650 nm. Peaks within this range can provide improved sensitivity to wavelengths that are more likely to indicate overheating of the resistance heating element.

[0031] The device may include a light guide comprising at least one reflective surface, the light guide being configured and positioned to transmit light from a resistive heating element to a photosensor. This allows the photosensor to be positioned further away from the resistive heating element, which can reduce the temperature experienced by the photosensor when the device is in operation.

[0032] The light guide may include at least two mirrors. This can provide an improved or at least alternative option for the path taken by light from the resistive heating element to the light sensor.

[0033] The light guide can be elongated in the direction roughly between the resistive heating element and the light sensor.

[0034] The device can be a hair styling tool or a heater. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a hair dryer-type device according to an embodiment of the present invention;

[0036] Figure 2 It shows the formation Figure 1 A graph showing the sensitivity curve of the optical sensor, which is part of the device.

[0037] Figure 3 yes Figure 1 A diagram of a hair dryer, including two accessories.

[0038] Figure 4 and Figure 5 It shows Figure 2 The sensitivity curves are marked with emission wavelengths for different heating element temperatures;

[0039] Figure 6 It shows the response to by Figure 1 The temperature signal output by the temperature sensor of the hair dryer Figure 1 A graph showing the output power of the hair dryer's drive circuit; and

[0040] Figures 7 to 11This is a schematic diagram illustrating various examples of optical guides that can be used with embodiments of the present invention. Detailed Implementation

[0041] Figure 1 A device in the form of a hair dryer 100 is shown. The hair dryer 100 is shown schematically, and the form, size, and relative positions of the components and features of a hair dryer manufactured according to the shown schematic diagram can be compared with... Figure 1 The difference is shown.

[0042] The hair dryer 100 includes a housing 102 that defines an air path 104 within the housing 102. The air path 104 includes an inlet 106 at a first end, and the inlet 106 includes an air filter 108 for reducing the amount of dust, lint, etc., entering the air path 104. The air filter 108 may be in the form of, for example, a mesh filter, multiple small holes formed in the housing, or a separate insert. The air path 104 also includes an outlet 110 through which air passes when the hair dryer 100 is in operation.

[0043] A resistance heating element 112 is disposed in the air path 104. The heating element 112 may be in the form of, for example, a metal heater, such as an open-wire heater. The wire may be formed of any suitable material, such as NiCr. The wire may be straight, coiled, or coiled, or may take any other form or profile.

[0044] An airflow generator 114 is also disposed in the air path 104, upstream of the heating element 112. The airflow generator 114 includes an electric motor 116 and a rotating impeller 118 connected to be driven by the electric motor 116, thereby generating an airflow within the air path 104 from the inlet 106 to the outlet 110 via the heating element 112.

[0045] The hair dryer 100 includes a handle 120 attached to and extending downward from a housing 102. The handle 120 includes a user interface 122 on its outer surface for allowing a user to control the operation of the hair dryer 100, including, for example, heat and air speed settings, as described in more detail below. The user interface 122 may also include visual, audio, and / or tactile communication elements (not shown) for providing feedback to the user regarding the operation of the hair dryer. Details of the user interface 122 are not shown, but it should be understood that any suitable combination of one or more buttons, sliders, knobs, screens, touchscreens, and lights may be provided depending on the implementation.

[0046] The handle 122 is at least partially hollow and contains a power source 124 that receives mains power from a power cable 126 that enters through the lower end of the handle 122. The power cable 126 terminates at a plug (not shown) that can be inserted into a mains outlet (not shown). The power source 124 includes an AC-DC converter (not shown) for converting AC mains power into one or more DC voltages for powering other components within the hair dryer 100.

[0047] In other embodiments, the device (e.g., a hair dryer or heater) may be battery powered, in which case a rechargeable battery or other battery may power the controller, airflow generator, heating element, and other components of the device.

[0048] A controller 128 for controlling various features and functions of the hair dryer 100 is disposed within the handle 122 and is connected to be powered by a power supply 124. The controller 128 includes a processor 130 and a memory 132 for storing instructions operable by the processor 130, as described in more detail below, as well as other functional elements, such as I / O circuitry for sending and receiving control signals and information from sensors within the hair dryer 100, including those described in more detail below. Although only a single controller 116 is shown for the hair dryer 100, it should be understood that the implementation of the features and components of the hair dryer 100 may be distributed across two or more processors, located within the housing 102, the handle 120, or externally, such as in a connected housing, or in any combination of these locations. For clarity, additional supporting circuitry, such as some sensors, communications, and power supplies, is omitted. An example of a suitable MCU is an ARM Cortex-M0+.

[0049] A controller 128 is connected to control a heater drive circuit 134 disposed within the handle 120. The heater drive circuit 134 may include, for example, one or more current control devices, such as a TRIAC (not shown), which the controller 128 may control to modulate the power output of the heating element 112. The drive circuit 134 is connected to receive mains power from a power cable 126. The drive circuit 134 may be operated by the controller 128 in a simple on / off manner, or it may be modulated across a range of power outputs to vary the temperature of the air leaving the outlet 110, including, for example, maintaining a constant temperature at different air output rates.

[0050] The controller 128 is also connected to control a motor controller 136 disposed within the handle 120. The motor controller 136 receives control signals from the controller 128, as described in more detail below, and outputs motor drive signals to the motor 116. Optionally, the motor drive signals may be connected to the motor via an electromagnetic compatibility (EMC) filter (not shown). This EMC filter filters out harmonics generated by the electric motor 116 during use.

[0051] For example, user interface 122 allows the user to set a target temperature and fan speed. The target temperature and fan speed can each be selected from a relatively small number of options (e.g., high, medium, and low settings for each of the target temperature and fan speed). Alternatively, either or both of the target temperature and fan speed can be selected in a more granular manner. For example, the target temperature can be selected as a specific temperature in degrees Celsius or Fahrenheit, with a resolution of, for example, 5°, 10°, or 20°. Similarly, the fan speed can be selected as a specific airflow rate, for example, in liters per second. The target temperature and fan speed are stored in memory 132. They can be persistently stored or reset to default values ​​each time the blower 100 is started. In other embodiments, the fan speed and / or temperature or heating element output can be fixed.

[0052] A light sensor 138 is disposed within the hair dryer 100 to receive light from the heating element 118. In the illustrated example, the light sensor 138 is positioned on a mount 140, which is located within a housing 102 to support the airflow generator 114. In this embodiment, the light sensor 138 is positioned downstream of the motor 116, facing approximately the same direction as the airflow within the air path 104. In other embodiments, the light sensor 138 may be positioned downstream of the heating element 118, looking backward at the heating element 118 from upstream, or at any other location that allows the light sensor 138 to "see" some or all of the heating element 118.

[0053] The light sensor 138 is also positioned approximately centrally relative to the cross-sectional area of ​​the housing 102, enabling it to "see" virtually all of the downstream heating elements 112, as shown by dashed line 160. The light sensor 138 can be configured to "see" the heating elements due to their shape, arrangement, and position.

[0054] Alternatively or additionally, one or more optical elements, such as light guides or lenses (e.g., fisheye lenses), may collect light and direct it to the light sensor 138. For example, as Figure 11As shown, a light guide 170 extends from the light sensor 138 into an opening through and at least partially through the heating element 112. The light guide 170 can be formed of borosilicate glass or any other suitable heat-resistant material that is transparent to the wavelength of interest. Light 176 captured by the light guide 170 is guided to the light sensor 138. The light guide 170 can rely on total internal reflection and / or can have a specular coating to ensure that light does not escape during its journey to the light sensor 138. The use of such an optical element reduces the need for the sensor itself to be capable of sensing over a wide angular range.

[0055] The light sensor 138 is configured to sense a wavelength range that is an appropriate subset of the visible spectrum, at least a portion of which includes wavelengths that indicate overheating of the resistive heating element.

[0056] The light sensor 138 can be configured to sense such a wavelength range in any suitable manner. In one implementation, a photodiode with sensitivity only within the desired wavelength range can be used. An example is the Osram® SFH2270R photodiode, with a peak detection at 560 nm and a wavelength detection range extending between 480 and 650 nm. This provides good sensitivity in the orange / red region, the color associated with overheating of the resistive heating element. Other wavelength ranges can be used, optionally centered around different peaks (if peaks exist), depending on the specific wavelengths expected to be generated by the heating element when it overheats. Figure 3 The sensitivity curve of the optical sensor 138 is shown.

[0057] The wavelength range can optionally have a lower cutoff wavelength of 550 nm. That is, the optical sensor (including any filter) can be relatively insensitive to wavelengths shorter than 500 nm. Filtering out shorter wavelengths can help reduce false alarms, such as those that might occur due to sunlight or artificial lighting leaking into the hair dryer 100 during use.

[0058] The wavelength range can optionally have an upper cutoff wavelength of 780 nm. This means the optical sensor can be relatively insensitive to wavelengths longer than 1200 nm. Filtering out longer wavelengths helps reduce false alarms caused by temperature changes that occur during normal operation of the hair dryer 100.

[0059] The detection peak in the wavelength range can optionally be concentrated between 550 nm and 650 nm. For reasons discussed below, the optical sensor peak can be selected to be close to (e.g., within + / -10% or + / -5%) the temperature that the hot spot is more likely to reach than the entire heating element.

[0060] Other types of optical sensors can also be used. For example, an optical sensor may include one or more photoresistors, photodiodes, or phototransistors.

[0061] Depending on the device type and / or implementation, a light sensor can be configured to sense a range of wavelengths due to its inherent characteristics. Alternatively, one or more filters (e.g., color filters) can be used to filter light incident on the device in order to effectively limit the wavelength range of its response. For example, a photodiode sensitive to the entire visible spectrum can be paired with an orange / red filter that transmits wavelengths indicating overheating of the resistive heating element while absorbing and / or reflecting at least a portion of the visible spectrum.

[0062] Any filter used may be included in the package of the device itself (i.e., covering the diode), or may take the form of a separate filter located between the heating element and the device to filter light passing through it. Optional light guides, lenses, reflectors, and other optical components described below may contain one or more such filters, in which case they may be considered part of the light sensor.

[0063] Such filters may be colored (e.g., using dyes or other colorants that induce the desired filter characteristics), and / or may contain interference or polarization properties.

[0064] The hair dryer 100 may optionally include support circuitry (not shown) connected to receive signals from the light sensor 138 and process them as needed. For example, such support circuitry may include one or more amplifiers and filters (e.g., high-pass, low-pass, band-pass, band-stop, and / or noise filters) that convert the raw signals from the light sensor 138 into a format more suitable for use by the controller 128. Such a format may include, for example, analog values ​​(e.g., voltage) or digital values ​​(e.g., numbers) that can be received and processed by the controller 128, optionally including further amplification and filtering, etc.

[0065] Alternatively, controller 128 may receive the raw signal from light sensor 138, sample it, and manipulate it in the digital domain (if needed).

[0066] In use, the light sensor 138 outputs a light signal in response to the intensity and wavelength of light incident upon it. The light signal is provided (optionally via support circuitry) to the controller 128. In the case where the light sensor 138 is a photodiode, the light signal may be a voltage representing the current currently passing through the light sensor 138, which represents the intensity and / or wavelength of the light incident on the sensor 138.

[0067] In use, the user can use the hair dryer 100 to dry their hair. The user interacts with the user interface 122 to select the heat settings and airflow rate. The controller 128 turns on the airflow generator 114 and the heating element 112 and controls them so that they output air at the correct temperature and speed.

[0068] When this occurs, some ambient light may be incident on the light sensor 138 due to light leakage, for example, through outlet 110. However, because the light sensor 138 is configured to sense the wavelength range indicating overheating of the resistive heating element, it does not respond to most ambient light. A small amount of light may fall on the light sensor 138, falling within the wavelength range that the light sensor 138 is configured to sense. However, the position and sensitivity of the light sensor 138, the interaction of any filters (not shown), and further processing by any supporting circuitry (not shown) can be configured to reduce false alarms.

[0069] Additionally, the hair dryer 100 can optionally be configured to operate only when the accessory is attached to the outlet 110. For example, Figure 3 A hair dryer 100 configured to accept various attachments is shown. When nothing is attached to outlet 110, processor 128 prevents operation of hair dryer 100 (specifically heating element 112 and airflow generator 114). When an attachment, such as diffuser 162 or concentrator 164, is attached to outlet 110 as indicated by arrow 166, a microswitch, reed switch, or other sensor (not shown) indicates to processor 128 that a compatible attachment has been attached to hair dryer 100. Processor 128 then allows operation of hair dryer 100.

[0070] For example, the accessories of diffuser 162 and concentrator 164 can reduce the amount of ambient light entering outlet 110. Moreover, even light entering through the accessories must travel a longer distance than it would if it could directly enter outlet 110. This can further help reduce false alarms caused by ambient light falling on light sensor 138.

[0071] According to the principle of blackbody radiation known to those skilled in the art, the wavelength of the radiation emitted by the heating element 112 changes when it is heated. During normal operation without overheating, the surface temperature of the heating element 112 is typically in the range of approximately 200 to 600°C. It should be understood that this range is a guideline and other temperatures and wavelengths may be applied depending on the implementation. Moreover, the temperature of the heating element may vary depending on factors such as the amount of local airflow it experiences and its proximity to heat-absorbing or reflective elements within the airflow path. At these temperatures during normal operation, the heating element 112 typically emits radiation in the infrared band and substantially no radiation in the wavelength range that the light sensor 138 is configured to sense.

[0072] Overheating involves an increase in visible light emission. As the temperature of the heating element 112 increases with the onset of overheating, the wavelength of the emitted radiation shortens. As the heating element 112 continues to overheat, the infrared radiation turns red, and then orange / red. In the described embodiment, the light sensor 138 is particularly sensitive to this orange / red color.

[0073] As the wavelength of the radiated light reaches the wavelength range sensitive to the light sensor 138, the light sensor 138 (which is a photodiode) begins to conduct current (exceeding the limited leakage current that would flow when the light sensor is not "on"). The current flows through a resistor (not shown), resulting in a voltage. This voltage is sensed by the controller 128.

[0074] When the voltage sensed by controller 128 rises to a predetermined level, the controller determines that heating element 112 is overheating and stops the drive current to heating element 112. Since drive current is required to keep heating element 112 hot as air is drawn onto it by airflow generator 114, heating element 112 will cool rapidly once the drive current stops. In other embodiments, the drive current may be reduced rather than stopped.

[0075] Optionally, the airflow generator can continue to operate to remove some of the excess heat from the overheated heating element 112. Alternatively, the airflow generator 114 can operate briefly and then shut down, or shut down immediately upon detecting overheating.

[0076] It should be understood that, according to the implementation, overheating can be determined based on the wavelength, intensity, or a combination of both sensed by the optical sensor 138.

[0077] For example, if the optical sensor 138 has a peak in its wavelength response, a wavelength at or near that peak can produce an optical signal with a similar intensity to a wavelength that is far from the peak but has a higher intensity.

[0078] Now refer to Figure 4 and Figure 5 An example illustrating this relationship is as follows: If all or most of the heating element overheats (e.g., due to overdrive caused by a malfunction elsewhere within the hair dryer 100), the relatively large surface area emits radiation at a similar average wavelength. As the heating element 112 becomes hotter and the average wavelength becomes shorter and eventually falls within the wavelength range of the photosensor 138, the relatively high power output resulting from the large emitting area generates a light signal sufficient to cause the aforementioned shutdown or power reduction. However, due to the relatively high power, the light signal can cause the controller 128 to shut down the heating element 112 before the average wavelength emitted by the heating element 112 reaches the peak sensitivity of the photosensor 138. (See reference...) Figure 4For example, overheating can be generated on virtually all surfaces of the heating element, producing an average emission wavelength of, for example, 600 nm (see vertical line 168), sufficient to cause the aforementioned shutdown or power limitation of the light signal.

[0079] Another form of overheating is a hot spot, where a relatively small area of ​​the heating element 112 becomes significantly hotter than the rest of the heating element. This can be caused, for example, by a localized short circuit within the heating element 112 or by a piece of debris obstructing localized airflow. Because such hot spots are relatively small, they may initially not output enough power to cause a shutdown or power limitation when the average wavelength shortens and falls within the sensor's wavelength range. However, as the temperature of the hot spot increases and the emitted wavelength decreases and shifts toward the sensor's sensitivity peak, the optical signal will increase. Even though the average power of the hot spot may be lower than the average power when the heating element is overheated overall, the additional sensitivity of the optical sensor to the higher temperature reached by the hot spot and the shorter average wavelength output means that the optical sensor still generates an optical signal sufficient to cause the aforementioned shutdown or power limitation. Reference Figure 5 For example, due to the relatively low power output of the hotspot, a hotspot that emits radiation with an average wavelength of 600 nm (such as...) Figure 4 (As shown) is insufficient to cause shutdown or power limiting. However, at 570 nm (see vertical line 172), despite the low power output of the hot spot, the greater sensitivity of the optical sensor 138 generates an optical signal sufficient to cause the aforementioned shutdown or power limiting.

[0080] The specific temperature and wavelength that will result in shutdown or reduced power, as well as the matching of the characteristics of the optical sensor with general heating element overheating and hot spot overheating, will be determined based on the implementation method. For example, various temperature / wavelength values ​​and ranges can be selected through, for example, modeling, experimentation, or both.

[0081] Back Figure 1 The hair dryer 100 may optionally include a temperature sensor. For example, a temperature sensor in the form of a thermistor 142 may optionally be disposed in the air path 104. The thermistor 142 is coupled to provide a temperature signal to the controller 128. Any other form of temperature sensor may be used to suit specific implementation requirements.

[0082] Thermistor 142 has a slower response time than the light sensor 138. This is generally a result of hysteresis introduced by the quality of thermistor 142, although other reasons for the slower response time are possible, depending on the type of temperature sensor and any supporting circuitry (not shown).

[0083] Thermistor 142 may optionally be used by the hair dryer 100 as part of its temperature control mechanism. Because it is located downstream of the heating element 112, it senses the temperature of the air shortly before the air leaves the outlet 110. The temperature signal provided by thermistor 142 to controller 128 can be used as feedback, allowing controller 128 to adjust the output of drive circuit 134 and / or motor drive controller 136 to maintain the air temperature at an appropriate level.

[0084] Thermistor 142 can also be used to identify overheating conditions. Although it does not directly sense the temperature of heating element 112, the temperature signal generated by thermistor 142 at least indirectly indicates that temperature. For example, in cases where airflow is restricted, such as through a blockage somewhere in air path 104, the reduced airflow to the current heat output of heating element 112 will cause the temperature at thermistor 142 to rise. Controller 128 can reduce the power output of heating element 112 by controlling drive circuitry 134, and / or attempt to increase airflow by controlling motor controller 136. However, if this is ineffective, controller 128 can determine that the temperature signal has been held too high for too long, indicating that the resistance heating element is overheating. In response, controller 128 can reduce or isolate the power to the resistance heating element.

[0085] Figure 6 Graph 144 shows how controller 128 controls the output power of drive circuit 134 in response to the temperature signal output by thermistor 142. Before the hair dryer 100 is first turned on via user interface 122 at time 200, thermistor 142 is at room temperature. At time 200, controller 128 causes drive circuit 134 to output maximum power to heating element 112, while also causing motor controller 136 to drive motor 116 and impeller 118 according to the currently selected airflow speed. After a brief lag, the temperature signal from thermistor 142 stabilizes at a continuously rising air temperature.

[0086] As the air temperature, determined by thermistor 142, rises, maximum power is maintained until the air temperature approaches the target temperature, which is 140°C in graph 144. Shortly before reaching this temperature (accounting for some expected overshoot), at time 202, the power decreases, resulting in a downward-sloping power line. As the temperature approaches the target temperature, the power continues to decrease. Once the temperature reaches the target temperature at time 204, the power is maintained at that level.

[0087] If the air temperature exceeds a target temperature, such as a certain threshold, the power is reduced to lower the air temperature toward the target air temperature. If the power reduction is ineffective, the air temperature may continue to rise. For example, in graph 144, the threshold temperature used to determine an overheating event is 150°C.

[0088] Heating element 112 begins to overheat, causing the temperature indicated by thermistor 128 to rise at time 206. Controller 128 responds by reducing power, but in this example, this is insufficient to stop the increase in heat, as shown by the continued increase in temperature after time 206.

[0089] Finally, at time 208, the temperature indicated by the thermistor reached 150°C. The processor 128 determined that an overheating event had occurred and shut off the power to the heating element 112.

[0090] Optionally, determining whether to significantly reduce or isolate the power to the heating element 112 based on the temperature signal can be based on the change of the temperature signal over time. For example, the temperature signal can be averaged or otherwise low-pass filtered to avoid transient temperature spikes that could cause false alarms.

[0091] The controller 128 can determine that at least a portion of the resistance heating element 112 is overheating based on either or both of the light and temperature signals. This provides improved safety. Not only do two different sensors operate to determine if the heating element is overheating, but they each have different and complementary advantages. For example, the thermistor 142 responds relatively slowly but can detect relatively small amounts of overheating. In contrast, the light sensor 138 responds relatively quickly but requires a larger temperature difference above the nominal operating temperature, at least in some cases, to cause power reduction or isolation. Thermistors 142 may react slowly to hot spots, especially if they are small, because hot spots may not raise the air temperature enough to indicate that overheating is occurring, while the light sensor 138 can identify hot spots more easily.

[0092] In one implementation, the light sensor is configured or optimized to identify hot spots, while the temperature sensor is configured or optimized to identify overheating of the entire heating element.

[0093] A potential advantage of using wavelength-based overheat sensors is that the same sensor can be used with different heating element materials that have different properties. For example, a nickel-chromium-based heating element will begin to emit visible light at a different temperature compared to an aluminum-based heating element. However, in both cases, the emission of visible light indicates overheating, and therefore the same sensor can be used with both types of heating elements.

[0094] Optionally, controller 128 may store indications that result in a reduction or isolation of power to the resistance heating element. For example, when power to the resistance heating element is reduced or isolated due to an overheating indication from a light signal, the controller may store this information in (non-volatile) memory 132. This information may then be used in a variety of ways.

[0095] For example, controller 128 can cause hair dryer 100 to enter a resistance heating element cleaning mode. In this mode, airflow generator 114 operates to control airflow through air path 104 in an attempt to remove potential blockages. Such blockages may reduce airflow, including excessive airflow above heating element 112 (which may cause overall overheating of element 112) and / or localized airflow above small heating areas within 112 (which may cause hot spots). The resistance heating element cleaning mode may include, for example, controlling motor 116 to rapidly change speed, reverse its rotation direction, and gradually accelerate and decelerate over a wide speed range.

[0096] Alternatively or additionally, the controller 128 may output, via the user interface 122, an instruction, for example, that the user should place the device in the resistance heating element cleaning mode as described above. This allows the user to control when this cleaning mode occurs.

[0097] Alternatively or additionally, the controller 128 may output, for example via the user interface 122, an indication of reduced or isolated power to the resistance heating element in response to a light signal. Alternatively, the controller 128 may also output, for example via the user interface 122, an indication of a fault condition and / or an indication that the device requires repair or maintenance. These options can alert the user to the need for maintenance or repair, whether performed by the user or by a suitable service center.

[0098] Although the light sensor 138 of the hair dryer 100 is mounted at a location that directly senses the temperature of the heating element 112, in other embodiments, the light sensor can be positioned further away from the heating element. In this case, the device may include a light guide that includes at least one reflective surface, and the light guide is configured and positioned to transmit light from the resistive heating element to the light sensor.

[0099] Depending on the implementation requirements, light guides can take several forms. Furthermore, the term "light guide" in this document simply means the space through which light is directed, and can include air or another transparent medium, such as glass or polymer. A light guide does not need to be defined by, for example, a wall or other structure.

[0100] Optionally, the light guide can be configured to filter certain wavelengths of light. For example, the light guide can take the form of a bandpass filter. Optionally, the bandpass filter is configured to allow at least some of the wavelengths mentioned above to pass through, in which case the light guide can be considered part of a light sensor.

[0101] Similarly, any reflective surface within a light guide can be configured to reflect certain wavelengths of light more strongly. For example, an interference reflector can be configured to reflect certain wavelengths of light more strongly. The reflective surface can be configured to allow at least some of the aforementioned wavelengths to pass through; in this case, the reflective surface can be considered part of a photosensitive sensor.

[0102] Go to Figures 7 to 10 The diagram shows detailed schematics of the components of various devices. These devices can be hair dryers, heaters, or any other devices that heat air using resistance heating elements.

[0103] Figure 7 A heating element 112 is shown, with a light sensor 138 positioned remotely from it. In this context, "remotely" means that the light sensor is too far from the heater to adequately sense its emission, or is positioned in a line-of-sight view without the heating element 112. A light guide 145 extends from a point adjacent to the heating element 112 to a point adjacent to the light sensor 138. The light guide 145 is in the form of a plate or cylinder made of a heat-resistant material such as glass (e.g., borosilicate glass) or a suitable polymer.

[0104] The first end 146 of the light guide 145 is at an angle of approximately 45°, and the second end 148 of the light guide 145 is similarly at an angle of approximately 45°. At least the angled portions of the first end 146 and the second end 148 are reflective and configured in a periscope arrangement, such that light 150 from the heating element 112, which enters laterally into the light guide 145 at the first end 146, is deflected along the light guide 145. When the light 150 strikes the second end 148, it is deflected again and exits laterally from the light guide 145. The light 150 exiting the light guide 145 at the second end 148 falls onto the photosensor 138, which behaves as described above.

[0105] Figure 8 It shows Figure 7 An alternative arrangement is provided, wherein the light guide includes a first reflector 152 positioned adjacent to the heating element 112 and a second reflector 154 positioned adjacent to the photosensor 138, and an air space between the first reflector 152 and the second reflector 154. The first and second reflectors 154 are angled in the same manner as the first and second ends 146 and 148 of the light guide 145. Figure 8 The operation of the light guide in the middle is similar to Figure 7 The operation is shown in the diagram. One difference is that, since light does not have to pass through a medium such as glass, Figure 8 The arrangement can have lower losses.

[0106] Figure 9 It shows Figure 7 and Figure 8 An alternative arrangement is provided, in which the light guide comprises only the first reflector 152 and the air path between it and the light sensor 138. In this case, the first reflector 152 reflects light 150 directly to the light sensor 138.

[0107] exist Figures 7 to 9In each of these components, the light guide is elongated approximately in the direction between the resistive heating element and the photosensor. It should be understood that more complex paths are possible, and the angle of the reflecting surface does not necessarily have to be, for example, 45°. The light guide may also comprise several light guide elements.

[0108] Figure 10 Another version of the light guide 145 is shown. In this case, the light guide 145 takes the form of a bundle of optical fibers extending from a first end 156 near the heating element 112 to a second end 158 near the photosensor 138. In this case, the air-fiber interface is the reflective surface due to total internal reflection occurring through this fiber. Any suitable number of optical fibers can be used.

[0109] Alternatively, one or more collimating lenses or reflectors can be used to focus more light emitted from the heating element 112 onto the first end 156, thereby increasing the amount of light reaching the light sensor 138 from the heating element 112. One example is... Figure 10 The collimating lens 174 shown focuses light from the heating element 112 into a smaller area, so that more light can enter the end of the optical fiber of the light guide.

[0110] The advantage of using optical fibers is that they can be bent into any shape (within reasonable limits), allowing them to move light through a potentially complex route between the heating element 112 and the light sensor 138.

[0111] It should be understood that different types, combinations, and configurations of light guides can be used. For example, a larger or more numerous reflective surfaces can be used. The outer surface of the light guide (e.g., light guide 145) can be coated and / or treated such that light is internally reflected within the light guide, which can increase the amount of light reaching the light sensor. Elements with focusing capabilities may be included. For example, one or more lenses and / or curved mirrors can be used to manipulate light from the heating elements. For example, collimating lenses or mirrors can be used to focus light from some or all of the heating elements to a smaller point, enabling the light sensor to sense light from more heating element surfaces.

[0112] Although various hair styling devices in the form of hair dryers have been described, and certain advantages arise from such use, it should be understood that the invention can also be applied to any other heated air device. Another example of such a device is a heater, such as a household space heater.

[0113] Although the invention has been described with reference to several specific embodiments and implementations, those skilled in the art will understand that the invention may be practiced in many other forms.

Claims

1. An apparatus comprising: Air path, which includes inlet and outlet; A resistance heating element, which is placed in the air path, is used to heat the air passing through the air path; An airflow generator is used to draw air in through an inlet, allow it to travel along an air path through a resistance heating element, and exit through an outlet. as well as A light sensor configured to receive light from a resistive heating element, the light sensor being configured to sense a wavelength range that is an appropriate subset of the visible spectrum, at least a portion of the wavelength range including wavelengths that indicate overheating of the resistive heating element; The device is configured such that the light sensor senses light within the wavelength range from the resistive heating element, resulting in a reduction or isolation of power to the resistive heating element.

2. The apparatus of claim 1, further comprising a controller coupled to receive an optical signal from the optical sensor and to control the resistive heating element, the controller being configured to: Receive optical signals from a light sensor, the optical signals indicating the wavelength and / or intensity of light generated by a resistive heating element; The overheating of the resistance heating element is determined based on the wavelength and / or intensity indicated by the optical signal; and In response to determining that the resistance heating element is overheating, the power to the resistance heating element is reduced or the resistance heating element is isolated.

3. The apparatus of claim 2, further comprising a temperature sensor having a slower response time than the optical sensor and coupled to provide a temperature signal to the controller, the controller being configured to: A temperature signal is received from a temperature sensor, the temperature signal indicating the temperature of at least a portion of the resistive heating element; Based on the temperature signal, it is determined that the resistance heating element is overheating; and In response to determining that the resistance heating element is overheating, the power supplied to the resistance heating element is reduced or isolated.

4. The apparatus according to claim 3, wherein, The controller is configured to reduce or isolate the power to the resistance heating element in response to determining, based on the optical signal, that at least a portion of the resistance heating element is overheating, regardless of whether the temperature signal indicates that the resistance heating element is overheating.

5. The apparatus according to claim 4, wherein: When the controller reduces or isolates the power to the resistance heating element in response to determining that at least a portion of the resistance heating element is overheating based on the optical signal, the controller causes the storage of an indication that the resistance heating element is reduced or isolated in response to the optical signal.

6. The apparatus according to claim 4 or 5, wherein: When the controller reduces or isolates the power to the resistance heating element in response to determining, based on the optical signal, that at least a portion of the resistance heating element is overheating, the controller: The device is put into a resistance heating element cleaning mode, wherein the airflow generator controls the airflow through the air path in an attempt to remove any blockages that may have caused localized hot spots on the resistance heating element, resulting in a light signal indicating that the resistance heating element is overheating; Output an instruction to the user that the device should be placed in the resistance heating element cleaning mode; It outputs an indication to the user that the power supplied to the resistance heating element is reduced or isolated in response to a light signal; Output fault status indications to the user; and / or The device is given an instruction to the user that it needs maintenance or repair.

7. The apparatus according to any one of the preceding claims, wherein, The wavelength range has a lower cutoff wavelength of 550 nm.

8. The apparatus according to any one of the preceding claims, wherein, The wavelength range has an upper cutoff wavelength of 780 nm.

9. The apparatus according to any one of the preceding claims, wherein, The detection peaks within the wavelength range are concentrated between 550 nm and 650 nm.

10. The apparatus according to any one of the preceding claims, comprising a light guide including at least one reflective surface, the light guide being configured and positioned to transmit light from the resistive heating element to the photosensor.

11. The apparatus according to claim 10, wherein, The light guide includes at least two mirrors.

12. The apparatus according to claim 10 or 11, wherein, The light guide is elongated in the direction generally between the resistive heating element and the photosensor.

13. The apparatus according to any one of the preceding claims, wherein, The device is a hair styling tool.

14. The apparatus according to any one of claims 1 to 12, wherein, The device is a heater.

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