Patent Description:
This specification relates to actuators that include one or more electro-magnetic coils and to panel audio loudspeakers that feature the actuators.

Many electronic devices are capable of presenting multimedia content by including speakers which provide tonal, voice-generated, or recorded output. Panel audio loudspeakers can produce sound by inducing distributed vibration modes in a panel through an electro-acoustic actuator. The panel can include a display panel, for example. Typically, the actuators are electro-magnetic or piezoelectric actuators.

This specification describes techniques, methods, systems, and other mechanisms for monitoring temperature of a panel in a panel audio device.

A panel audio loudspeaker can include an actuator including a magnetic coil that provides a force to a panel, causing the panel to vibrate to produce audible sound waves. The magnetic coil of the actuator may be in thermal communication with the panel, such that heat can flow between the magnetic coil and the panel. For example, the coil can be affixed to a surface of the panel, e.g., by an adhesive.

The panel may be, for example, a display panel of a mobile telephone, smart watch, or head-mounted display. It is desirable to predict, measure, and monitor a temperature of the panel. High panel temperatures may cause injury to a user, and may cause damage to the panel and connected components. For example, it may be desirable to maintain a panel temperature below <NUM> degrees Celsius to reduce risk of injury and damage.

During actuator operation, a control module for a panel audio loudspeaker can provide an electrical audio signal to the magnetic coil, and can measure electrical data for the magnetic coil. Based on the electrical data, the control module can determine an amount of energy applied to the magnetic coil during a period of time. Based on the amount of energy applied to the magnetic coil, a thermal model of the panel, and an initial temperature, the control module can determine a final temperature of the panel.

The control module may determine that the final temperature of the panel violates a limit or threshold temperature. In response to determining that the final temperature of the panel violates the threshold temperature, the control module can adjust the audio signal supplied to the magnetic coil. For example, the control module may reduce the current of the audio signal supplied to the magnetic coil. Reducing the current of the audio signal supplied to the magnetic coil may cause the panel temperature to increase at a slower rate, to cease increasing, or to decrease.

In general, one innovative aspect of the subject matter described in this specification can be embodied in a panel audio loudspeaker, including: a panel; an actuator attached to a surface of the panel and configured to cause vibration of the panel, the actuator including a magnetic coil in thermal communication with the panel; a plurality of electrical sensors electrically coupled to the magnetic coil and configured to output time-varying electrical data for the magnetic coil; and an electronic control module in communication with the magnetic coil and the plurality of electrical sensors. The electronic control module is configured to perform operations including: providing a current to the magnetic coil; receiving, from the plurality of electrical sensors, the time-varying electrical data for the magnetic coil; based on the time-varying electrical data for the magnetic coil, determining an electrical energy provided to the magnetic coil between a first time and a second time; accessing a thermal model of the panel; and based on the electrical energy provided to the magnetic coil, and the thermal model of the panel, determining a change in a panel temperature between the first time and the second time.

The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In some implementations, the time-varying electrical data includes one or more of: a time-varying current through the magnetic coil; and a time-varying voltage across the magnetic coil.

In some implementations, the thermal model of the panel includes one or more of: data representing heat transfer from the magnetic coil to the panel; and data representing heat transfer from the panel to ambient.

In some implementations, the thermal model of the panel includes an association curve between the electrical energy provided to the magnetic coil and the change in the panel temperature.

In some implementations, determining the electrical energy provided to the magnetic coil includes: determining, from the time-varying electrical data for the magnetic coil, a time-varying power provided to the magnetic coil; and integrating the time-varying power between the first time and the second time.

In some implementations, the operations further include: determining, from the time-varying electrical data for the magnetic coil and the thermal model of the panel, a first panel temperature at the first time; based on the first panel temperature, and the change in the panel temperature between the first time and the second time, determining a second panel temperature at the second time; and based on the second panel temperature, adjusting the current provided to the magnetic coil.

In some implementations, the operations further include: determining, from the change in the panel temperature between the first time and the second time, a rate of change of the panel temperature; and based on the rate of change of the panel temperature, adjusting the current provided to the magnetic coil.

In some implementations, the electronic control module includes one or more of an audio signal source, an amplifier, and a digital signal processor.

In some implementations, the panel includes a display panel.

In general, one innovative aspect of the subject matter described in this specification can be embodied in a mobile device, including a housing and the panel audio loudspeaker.

In some implementations, the mobile device includes a mobile phone or a tablet computer.

In general, one innovative aspect of the subject matter described in this specification can be embodied in a wearable device, including a housing and the panel audio loudspeaker.

In some implementations, the wearable device is a smart watch or a head-mounted display.

In general, one innovative aspect of the subject matter described in this specification can be embodied in a method including: providing a current to a magnetic coil of an actuator to cause vibration of a panel, the magnetic coil being in thermal communication with the panel; receiving, from a plurality of electrical sensors electrically coupled to the magnetic coil, time-varying electrical data for the magnetic coil; based on the time-varying electrical data for the magnetic coil, determining an electrical energy provided to the magnetic coil between a first time and a second time; accessing a thermal model of the panel; and based on the electrical energy provided to the magnetic coil, and the thermal model of the panel, determining a change in a panel temperature between the first time and the second time.

In some implementations, the method further includes: determining, from the time-varying electrical data for the magnetic coil and the thermal model of the panel, a first panel temperature at the first time; based on the first panel temperature, and the change in the panel temperature between the first time and the second time, determining a second panel temperature at the second time; and based on the second panel temperature, adjusting the current provided to the magnetic coil.

In some implementations, the method further includes: determining, from the change in the panel temperature between the first time and the second time, a rate of change of the panel temperature; and based on the rate of change of the panel temperature, adjusting the current provided to the magnetic coil.

In some implementations, the method further includes: adjusting the current provided to the magnetic coil includes reducing the current provided to the magnetic coil.

In general, actuator modules can be used in a variety of applications. For example, in some embodiments, an actuator module can be used to drive a panel of a panel audio loudspeaker, such as a distributed mode loudspeaker (DML). Such loudspeakers can be integrated into a mobile device, such as a mobile phone, a smart watch, or a head-mounted display. For example, referring to <FIG>, a mobile device <NUM> includes a device chassis <NUM> and a panel <NUM> including a flat panel display (e.g., an OLED or LCD display panel) that integrates a panel audio loudspeaker. Mobile device <NUM> interfaces with a user in a variety of ways, including by displaying images and receiving touch input via panel <NUM>. Typically, a mobile device has a depth (in the z-direction) of approximately <NUM> or less, a width (in the x-direction) of <NUM> to <NUM> (e.g., <NUM> to <NUM>), and a height (in the y-direction) of <NUM> to <NUM> (e.g., <NUM> to <NUM>). A Cartesian coordinate system is shown in <FIG> for reference.

The mobile device <NUM> also produces audio output. The audio output is generated using a panel audio loudspeaker that creates sound by causing the flat panel display to vibrate. The display panel is coupled to an actuator, such as a distributed mode actuator, or DMA. The actuator is a movable component arranged to provide a force to a panel, such as the panel <NUM>, causing the panel to vibrate. The vibrating panel generates human-audible sound waves, e.g., in the range of <NUM> to <NUM>.

Generally, the efficiency of the actuator to produce audible sound waves varies as a function of frequency depending on the properties of the actuator, the panel, and the coupling of the actuator to the panel. Typically, the actuator/panel system will exhibit one or more resonant frequencies representing frequencies at which the sound pressure level as a function of frequency has a local maximum. It is generally desirable, however, for a panel audio loudspeaker to maintain a relatively high sound pressure level across the entire audio frequency spectrum.

In addition to producing sound output, the mobile device <NUM> can also produce haptic output using the actuator. For example, the haptic output can correspond to vibrations in the range of <NUM> to <NUM>.

<FIG> also shows a dashed line that corresponds to the cross-sectional direction shown in <FIG>. Referring to <FIG>, a cross-section of mobile device <NUM> illustrates device chassis <NUM> and the panel <NUM>. <FIG> also includes a Cartesian coordinate system with x, y, and z axes, for ease of reference. The device chassis <NUM> has a depth measured along the z-direction and a width measured along the x-direction. The device chassis <NUM> also has a back panel, which is formed by the portion of device chassis <NUM> that extends primarily in the x-y plane. The mobile device <NUM> includes the actuator module <NUM>, which is housed behind the panel <NUM> in the chassis <NUM> and attached to the back side of the panel <NUM>. A pressure sensitive adhesive (PSA) <NUM> can attach the actuator module <NUM> to the panel <NUM>. Generally, the actuator module <NUM> is sized to fit within a volume constrained by other components housed in the chassis, including an electronic control module <NUM> and a battery <NUM>.

The actuator module <NUM> can be configured to convert electrical energy into acoustic energy. The actuator module <NUM> can be controlled by the electronic control module <NUM>. The electronic control module <NUM> can be composed of one or more electronic components that receive input from one or more sensors and/or signal receivers of the mobile device <NUM>, process the input, and generate and deliver signal waveforms that cause actuator module <NUM> to provide a suitable haptic response. The electronic control module <NUM> can be in communication with the magnetic coil <NUM>.

Referring to <FIG>, the actuator module <NUM> includes a magnetic coil <NUM> and the PSA <NUM>. The PSA <NUM> allows the actuator module <NUM> to be affixed to the panel <NUM>. The actuator module <NUM> can be relatively compact. For example, the actuator module's height (i.e., its dimension in the z-direction) can be about <NUM> or less (e.g., <NUM> or less, <NUM> or less, <NUM> or less).

During operation, the electronic control module <NUM> energizes the magnetic coil <NUM> by applying an electric current to the magnetic coil <NUM>. The resulting magnetic flux interacts with a suspended magnet, and the resulting vibrations are transferred to the panel <NUM>.

The magnetic coil <NUM> can be constructed using a thin wire that is suspended within a magnetic field generated by a magnet. When an analog signal, which can be an input voltage signal, passes through the magnetic coil <NUM>, an electro-magnetic field is produced. The electro-magnetic field signal strength is determined by the current flowing through coil.

The magnetic coil <NUM> is attached to a surface of the panel <NUM>, which also moves in tandem. The magnetic coil <NUM> may be affixed to the surface of the panel <NUM> by an adhesive, e.g., a pressure sensitive adhesive, a liquid adhesive, etc. Movement of the panel can cause a disturbance in the air around it, thus producing a sound. In the instances where the input signal is a sine wave, then the panel <NUM> will pulsate (e.g., in and out) which pushes air as it moves, and generates an audible tone, representing the frequency of the signal. The strength, and therefore the velocity, by which the panel <NUM> moves and pushes the surrounding air may be determined at least in part based on the input signal applied to the magnetic coil <NUM>.

The magnetic coil <NUM> can be in thermal communication with the panel <NUM>. When in thermal communication with the panel, heat can flow, or transfer, from the magnetic coil <NUM> to the panel <NUM>, and from the panel <NUM> to the magnetic coil <NUM>. For example, when the electronic control module <NUM> drives the magnetic coil <NUM>, current flows through the magnetic coil <NUM>, heating the magnetic coil <NUM>. Heat from the magnetic coil <NUM> may then transfer to the panel <NUM>.

During operation of the actuator module <NUM>, a magnetic coil temperature may rise, causing a panel temperature to also rise. As the panel <NUM> receives heat from the magnetic coil <NUM>, the panel <NUM> may also lose heat to ambient. Thus, during operation, the panel temperature may rise at a slower rate of change than the magnetic coil temperature, and the panel temperature may remain lower than the magnetic coil temperature.

When the actuator module <NUM> is not in operation, the magnetic coil temperature may fall, causing the panel temperature to also fall. During an extended time when the actuator module <NUM> is not in operation, the magnetic coil <NUM> and the panel <NUM> may reach thermal equilibrium. Thus, when current has not passed through the magnetic coil <NUM> for an extended period of time, the magnetic coil <NUM> and the panel <NUM> may reach the same temperature.

<FIG> is a diagram of an example system <NUM> configured to monitor temperature of a panel in a panel audio device. The system <NUM> includes the electronic control module <NUM>, the magnetic coil <NUM>, and the panel <NUM>. The electronic control module <NUM> includes a signal generator <NUM>, a processor <NUM>, a digital-to-analog converter (DAC) <NUM>, an amplifier <NUM>, a current sensor <NUM>, a current analog-to-digital converter (ADC) <NUM>, a voltage sensor <NUM>, a voltage ADC <NUM>, a clock <NUM>, and a memory <NUM> that can store a panel thermal model <NUM> and an initial panel temperature <NUM>.

Though a particular configuration of the system <NUM> is shown in <FIG>, other configurations are possible. For example, in some implementations, certain components might not be included in the electronic control module <NUM> as shown. For example, the signal generator <NUM>, the clock <NUM>, and/or the amplifier <NUM> might not be included in the electronic control module <NUM>. In some implementations, certain components may be combined into a single component. For example, the amplifier <NUM> may include the processor <NUM>, the DAC <NUM>, or both. In some examples, the processor <NUM> may include the memory <NUM>, the DAC <NUM>, the current ADC <NUM>, the voltage ADC <NUM>, or all of these.

In general, operations of the system <NUM> are as follows. The magnetic coil <NUM> can be in communication with the electronic control module <NUM>, e.g., through a wired or wireless connection. The magnetic coil <NUM> can receive, as input, an electrical signal that has been output from the amplifier <NUM>. As the electrical signal is applied to the magnetic coil <NUM>, the magnetic coil temperature may rise, and in tum, the panel temperature may also rise.

Electrical sensors can measure time-varying electrical data for the magnetic coil <NUM>. For example, the current sensor <NUM> can measure a time-varying current through the magnetic coil <NUM>, and the voltage sensor <NUM> can measure a time-varying voltage across the magnetic coil <NUM>. The processor <NUM> can determine an amount of energy supplied to the magnetic coil <NUM> over a period of time, based on the measured coil current and coil voltage. Based on the supplied energy, the panel thermal model <NUM>, and the initial panel temperature <NUM>, the processor <NUM> can determine a final temperature of the panel <NUM>. Based on the final temperature of the panel <NUM>, the processor <NUM> may determine to adjust the electrical signal provided to the magnetic coil <NUM>.

The signal generator <NUM> can be an audio signal source that generates an audio signal. For example, the signal generator can generate a digital audio signal representing an audible sound to be produced by the panel <NUM>.

The processor <NUM> can be, for example, a digital signal processor (DSP). The processor <NUM> can receive the audio signal from the signal generator <NUM>. The processor <NUM> can process the audio signal, for example, by decoding, filtering, decompressing, transforming, and modulating the audio signal. In some examples, the processor <NUM> can adjust the audio signal by increasing or decreasing a power level of the audio signal. The processor <NUM> can output an adjusted digital audio signal to the DAC <NUM>.

The DAC <NUM> can convert the digital audio signal to an analog electrical signal. The analog electrical signal can be, for example, an alternating current (AC) electrical signal. The DAC <NUM> can output the analog electrical signal to the amplifier <NUM>.

The amplifier <NUM> can amplify the analog electrical signal. For example, the amplifier <NUM> can amplify the analog electrical signal by increasing the voltage, current, or power of the analog signal. The amplifier <NUM> can output the amplified electrical signal to the magnetic coil <NUM>.

The magnetic coil <NUM> is energized by the amplified electrical signal output by the amplifier <NUM>. As current from the amplified electrical signal flows through the magnetic coil <NUM>, the magnetic coil temperature may rise. The panel <NUM>, in thermal communication with the magnetic coil <NUM>, may receive heat transferred from the magnetic coil <NUM>, causing the panel temperature to rise.

The current sensor <NUM> can measure electrical current flowing through the magnetic coil <NUM>. The current sensor <NUM> can be any appropriate type of current sensor. For example, the current sensor <NUM> may be a flux gate, hall-effect, or inductive current sensor. The current sensor <NUM> can output an analog signal representing the measured current to the current ADC <NUM>. The current ADC <NUM> can convert the analog signal representing the measured coil current to a digital current signal. The current ADC <NUM> can output the coil current to the processor <NUM>.

In some examples, the current sensor <NUM> may output a digital signal representing the measured coil current. In these examples, the system <NUM> might not include the current ADC <NUM>, and the current sensor <NUM> may provide the coil current directly to the processor <NUM>.

The voltage sensor <NUM> can measure voltage across the magnetic coil <NUM>. The voltage sensor <NUM> can be any appropriate type of voltage sensor. For example, the voltage sensor <NUM> may be a resistive or capacitive voltage sensor. The voltage sensor <NUM> can output an analog signal representing the measured voltage to the voltage ADC <NUM>. The voltage ADC <NUM> can convert the analog signal representing the measured voltage to a digital voltage signal. The voltage ADC <NUM> can output the coil voltage to the processor <NUM>.

In some examples, the voltage sensor <NUM> may output a digital signal representing the measured coil voltage. In these examples, the system <NUM> might not include the voltage ADC <NUM>, and the voltage sensor <NUM> may provide the coil voltage directly to the processor <NUM>.

The processor <NUM> can receive the coil current and the coil voltage from the current ADC <NUM> and the voltage ADC <NUM>. The processor <NUM> can determine the panel temperature based on the coil current and the coil voltage. Determining the panel temperature based on the coil current and the coil voltage is described with reference to <FIG>.

Referring to <FIG>, the processor <NUM> includes a power calculator <NUM>, an energy calculator <NUM>, a temperature change calculator <NUM>, a panel temperature calculator <NUM>, a panel temperature limiter <NUM>, and a signal adjuster <NUM>. The processor <NUM> can also optionally include a temperature rate of change calculator <NUM>.

The power calculator <NUM> of the processor <NUM> can receive a time-varying coil current <NUM> and a time-varying coil voltage <NUM> from the current ADC <NUM> and the voltage ADC <NUM>, respectively. The coil current <NUM> can be indicated, for example, in a unit of Amperes (A). The coil voltage can be indicated, for example, in a unit of Volts (V). Based on the coil current <NUM> and the coil voltage <NUM>, the power calculator <NUM> can calculate a power <NUM> of the magnetic coil <NUM>. Specifically, the power calculator <NUM> can multiply the coil current <NUM> and the coil voltage <NUM> at a particular time to calculate the power <NUM> at the particular time. The power calculator <NUM> may continuously calculate the time-varying power <NUM>. The power <NUM> can be indicated, for example, in a unit of Watts (W). An example graph of time-varying power <NUM> is shown in <FIG>.

Referring to <FIG>, the power <NUM> can be represented on a graph as a function of time. In general, the power <NUM> may increase, decrease, or remain steady over time while the actuator module <NUM> is in operation. For example, the audio signal may increase and decrease in power over time due to changes in audio volume, e.g., music or voice volume.

In <FIG>, the power <NUM> is graphed over a period of time that includes a first time <NUM> and a second time <NUM>. The first time <NUM> can be, for example, a period of time shortly after initially energizing the magnetic coil <NUM>. The second time <NUM> can be a time later than the first time <NUM>.

The energy calculator <NUM> of the processor <NUM> can receive the time-varying power <NUM> from the power calculator <NUM>. The energy calculator <NUM> can also receive a clock time <NUM> from the clock <NUM>. Based on the varying power <NUM> over time, the energy calculator <NUM> can calculate an energy <NUM> supplied to the magnetic coil <NUM>. Specifically, as shown in <FIG>, the energy calculator <NUM> can integrate the time-varying power <NUM> between the first time <NUM> and the second time <NUM> to determine the total energy <NUM> supplied between the first time <NUM> and the second time <NUM>.

In <FIG>, the energy <NUM> is represented by an area under the curve representing the time-varying power <NUM>. The energy <NUM> can be indicated, for example, in a unit of Joules (J). In general, higher power levels maintained over longer periods of time result in a larger area under the curve, and thus larger amounts of energy supplied to the magnetic coil. The energy calculator <NUM> can output the energy <NUM> to the temperature change calculator <NUM>.

The temperature change calculator <NUM> can receive the energy <NUM> from the energy calculator <NUM>, and the panel thermal model <NUM> from the memory <NUM>. In some examples, the panel thermal model <NUM> can be an experimental model. For example, experiments can be performed on the panel <NUM> or a similar panel to determine panel temperature behavior in response to energization of the magnetic coil <NUM>. Experiments can include energizing the magnetic coil <NUM> at known power levels for various time durations, and measuring a resulting temperature of the panel <NUM>. The resulting temperature of the panel <NUM> may be measured, for example, directly using a temperature sensor, or indirectly based on a resistance of the magnetic coil. In some examples, the electronic control module can determine that the magnetic coil <NUM> and the panel are likely at approximately the same temperature.

<FIG> shows an example temperature characteristic curve for the panel <NUM>. The characteristic curve can be generated by energizing the magnetic coil <NUM> with an audio signal at a steady, known power for a time duration, and then turning the audio signal off. As shown in <FIG>, panel temperature <NUM> and actuator temperature <NUM> can be represented on a graph as a function of time. Temperature change <NUM> can be indicated, for example, in a unit of degrees Celsius (°C). At time <NUM>, the audio signal turns on and energizes the magnetic coil <NUM> at a constant power. At time <NUM>, the audio signal turns off.

Between time <NUM> and time <NUM>, the actuator temperature <NUM> and the panel temperature <NUM> rise. For example, the actuator temperature <NUM> rises due to being energized by the audio signal, and the panel temperature <NUM> rises due to heat transfer from the magnetic coil <NUM>. The actuator temperature <NUM> may change temperature more rapidly than the panel temperature <NUM>, due to the magnetic coil <NUM> having a lower thermal mass than the panel <NUM>. After time <NUM>, when the audio signal is off, the actuator temperature <NUM> and the panel temperature <NUM> fall.

Temperature characteristic curves may be generated for various power levels and durations of time. From the temperature characteristic curves, the processor <NUM> can obtain a temperature rate of change for a particular power level at a given temperature. For example, the temperature characteristic curves can indicate that the panel temperature <NUM> changes <NUM> degree Celsius (°C) per minute per Watt at an initial temperature of <NUM>. Temperature characteristic curves for the panel <NUM> may be generated experimentally and stored in the memory <NUM>.

In some examples, the panel thermal model <NUM> can be a mathematical model. For example, the panel thermal model <NUM> can include data representing heat transfer from the magnetic coil <NUM> to the panel <NUM>, data representing heat transfer from the panel <NUM> to ambient, or both. The panel thermal model <NUM> can also include a model of panel temperature behavior in response to energization of the magnetic coil <NUM>. The data may account for factors such as the specific heat capacity of the panel <NUM>, the surface area of contact between the magnetic coil <NUM> and the panel <NUM>, and the total surface area of the panel <NUM>. The data may also account for factors such as changes in ambient temperature, changes in panel vibration frequency, and continuity of energization.

In some examples, the panel thermal model <NUM> can be a mathematical model that can be updated and verified experimentally. For example, the panel thermal model <NUM> can be generated mathematically for predicted panel temperature. Experiments can then be performed on the panel <NUM> or a similar panel to verify and/or update the panel thermal model <NUM>. Experiments can include energizing the magnetic coil <NUM> at steady power levels for various time durations and generating a temperature characteristic curves as shown in <FIG>. The resulting temperature of the panel <NUM> can be provided as feedback to the panel thermal model <NUM> in order to update the mathematical model.

In some examples, the panel thermal model <NUM> can be calibrated during a calibration phase of operation. For example, a preliminary thermal model may be programmed into the memory <NUM>. During the calibration phase, the electronic control module <NUM> can energize the magnetic coil <NUM> at known power levels, and the panel temperature can be measured. The panel thermal model <NUM> can then be updated based on the panel temperature measured during the calibration phase.

In some examples, instead of, or in addition to, the calibration phase, the panel thermal model <NUM> may continue to update during operation. For example, an audio signal may be applied to the magnetic coil <NUM> between a first time and a second time. While the audio signal is applied to the magnetic coil <NUM>, the actuator temperature <NUM> and the panel temperature <NUM> rise.

During a time duration between a second time and a third time, the audio signal may be off, or may be reduced to a lower power, such that heat from the actuator is no longer causing the panel temperature <NUM> to rise. The time duration may be equal to or longer than a threshold duration during which the actuator temperature <NUM> becomes approximately equal to the panel temperature <NUM>. The processor <NUM> can then measure the resistance of the magnetic coil <NUM> to determine the actuator temperature <NUM>, and therefore determine a measured panel temperature.

The processor <NUM> can also determine a calculated panel temperature at the third time based on the panel thermal model <NUM>. The processor <NUM> can then compare the measured panel temperature based on the actuator temperature <NUM> to the calculated panel temperature based on the thermal model. The processor <NUM> can calculate an error between the measured panel temperature and the calculated panel temperature. The processor <NUM> can provide the error as feedback to adjust one or more variables of the panel thermal model <NUM>.

In an example, an initial panel temperature <NUM> is <NUM>. An audio signal is applied to the magnetic coil <NUM> between a first time T1 and a second time T2. At time T2, the audio signal turns off and remains off until time T3. The time duration between T2 and T3 is a time duration longer than the threshold duration during which the actuator temperature <NUM> becomes approximately equal to the panel temperature <NUM>.

The processor <NUM> measures the resistance of the magnetic coil <NUM> at time T3. Based on the resistance, the processor determines an actuator temperature of <NUM>, and therefore a measured panel temperature of <NUM>. The processor <NUM> determines a calculated panel temperature of <NUM> based on the panel thermal model <NUM>. The processor <NUM> calculates an error of <NUM>. The processor <NUM> provides the error as feedback to adjust the panel thermal model <NUM>.

At the third time, the audio signal may again be applied to the magnetic coil <NUM>. The processor <NUM> can use the measured temperature at the third time as the initial panel temperature <NUM> for a next calculation of final panel temperature <NUM>. In the above example, the measured panel temperature of <NUM> can be used as the initial panel temperature <NUM> for the next calculation of final panel temperature <NUM>, e.g., the panel temperature at a fourth time T4.

In some examples, the panel thermal model <NUM> can include a panel thermal model curve <NUM> representing an association between energy and panel temperature change, as shown in <FIG>. The panel thermal model curve <NUM> may be generated based on temperature characteristic curves as shown in <FIG>. For example, the temperature characteristic curve can provide temperature rate of change for a particular power level at a given temperature. From multiple temperature characteristic curves, the temperature rate of change for an amount of energy may be determined. In some examples, multiple panel thermal model curve <NUM> may be generated for multiple initial temperatures.

Referring to <FIG>, the panel thermal model curve <NUM> can be represented on a graph as a function of energy. In general, the panel temperature change increases with increased energy, e.g., for a greater amount of energy supplied to the magnetic coil <NUM>, the panel temperature may change a greater amount. Though <FIG> shows a curve with an approximately logarithmic shape, the shape of the panel thermal model curve <NUM> may vary depending on characteristics of the panel. The shape of the panel thermal model curve <NUM> may be, for example, linear, exponential, or parabolic.

The panel thermal model <NUM> can be programmed into the memory <NUM>. The processor <NUM> can then access the panel thermal model <NUM> from the memory <NUM> in order to determine the panel temperature change <NUM>.

Using the panel thermal model curve <NUM>, the temperature change calculator <NUM> can calculate a panel temperature change associated with the energy <NUM>. In the example of <FIG>, the temperature change calculator <NUM> calculates a panel temperature change <NUM>. The panel temperature change <NUM> represents the change in panel temperature between the first time <NUM> and the second time <NUM>. The temperature change calculator <NUM> can output the panel temperature change <NUM> to the panel temperature calculator <NUM>.

The panel temperature calculator <NUM> can receive the panel temperature change <NUM> from the temperature change calculator <NUM>, and the initial, or first, panel temperature <NUM> from the memory <NUM>. The initial panel temperature <NUM> can be the panel temperature at the first time <NUM>. In some examples, at or before the first time <NUM>, the processor <NUM> can determine the initial panel temperature <NUM>, and store the initial panel temperature <NUM> in the memory <NUM>.

In some examples, the processor <NUM> can determine the initial panel temperature <NUM> based on the magnetic coil temperature at the first time <NUM>. In some examples, the panel thermal model <NUM> can include an association between the panel temperature and the magnetic coil temperature.

In some examples, the processor <NUM> can determine that the panel temperature is likely the same as the magnetic coil temperature. For example, based on the panel thermal model <NUM>, the processor <NUM> may determine that when the magnetic coil <NUM> is not energized for a certain duration of time, the panel <NUM> reaches a temperature that is the same, or approximately the same, as the magnetic coil temperature. The processor <NUM> can therefore determine, based on the magnetic coil <NUM> not being energized for the certain duration of time, that the initial panel temperature <NUM> is the same as the magnetic coil temperature.

In some examples, the first time <NUM> may be a time shortly after initially energizing the magnetic coil <NUM> following the certain duration of time that the magnetic coil <NUM> is not energized. In these examples, the processor <NUM> may determine that the initial panel temperature <NUM> at the first time <NUM> is the same as the magnetic coil temperature at the first time <NUM>.

In some examples, the processor <NUM> can determine the magnetic coil temperature based on a resistance of the magnetic coil <NUM> during operation of the actuator module <NUM>. For example, the processor <NUM> may determine the resistance of the magnetic coil <NUM> based on the coil current <NUM> and the coil voltage <NUM> while the actuator module <NUM> is operating. The magnetic coil <NUM> may have a known temperature coefficient of resistance. Thus, based on the resistance of the magnetic coil <NUM>, the processor <NUM> can determine the magnetic coil temperature. Based on the association between the magnetic coil temperature and the panel temperature, the processor <NUM> can determine the initial panel temperature <NUM>.

In some examples, the processor <NUM> can determine the magnetic coil temperature based on a resistance of the magnetic coil <NUM> when the actuator module <NUM> is not operating. For example, the processor <NUM> can provide a pilot tone to the magnetic coil <NUM>. The pilot tone can be, for example, a low amplitude and/or low frequency tone that does not cause the panel <NUM> to produce an audible sound. The processor <NUM> can measure the coil current <NUM> and the coil voltage <NUM> while the magnetic coil <NUM> is energized with the pilot tone. Based on the resistance of the magnetic coil <NUM> and the known temperature coefficient of resistance, the processor <NUM> can determine the magnetic coil temperature. Based on the association between the magnetic coil temperature and the panel temperature, the processor <NUM> can determine the initial panel temperature <NUM>.

In some examples, the initial panel temperature <NUM> can be a previously calculated final panel temperature <NUM>. For example, the processor <NUM> may determine the final panel temperature <NUM> at a second time <NUM>, based on the energy <NUM> and the panel thermal model <NUM>. The processor <NUM> may store the final panel temperature <NUM> at the second time <NUM> in the memory <NUM>, for later reference as an initial panel temperature <NUM> in a new calculation of final panel temperature <NUM>.

Based on the initial panel temperature <NUM> and the panel temperature change <NUM>, the panel temperature calculator <NUM> can calculate the final, or second, panel temperature <NUM>. The final panel temperature <NUM> can be the temperature of the panel <NUM> at the second time <NUM>. The panel temperature calculator <NUM> can calculate the final panel temperature <NUM>, for example, by adding the panel temperature change <NUM> to the initial panel temperature <NUM>. The panel temperature calculator <NUM> can output the final panel temperature <NUM> to the panel temperature limiter <NUM>.

The panel temperature limiter <NUM> can compare the final panel temperature <NUM> to a threshold panel temperature. The threshold can be, for example, a maximum allowable panel temperature. In some examples, the threshold panel temperature can be a panel temperature within a buffer range to the maximum allowable panel temperature. For example, a maximum allowable panel temperature may be <NUM>. To provide a buffer range of <NUM>, the threshold panel temperature may be set to <NUM>.

In some implementations, the temperature change calculator <NUM> can output the panel temperature change <NUM> to the temperature rate of change calculator <NUM> in addition to the panel temperature calculator <NUM>. Based on the panel temperature change <NUM> and the time duration between the first time <NUM> and the second time <NUM>, the temperature rate of change calculator <NUM> can determine the panel temperature rate of change <NUM>. The panel temperature rate of change <NUM> can be indicated, for example, in a unit of degrees Celsius per minute (°C/min). The temperature rate of change calculator <NUM> can output the temperature rate of change <NUM> to the panel temperature limiter <NUM>.

The panel temperature limiter <NUM> can compare the temperature rate of change <NUM> to a threshold temperature rate of change. The threshold can be, for example, a maximum allowable temperature rate of change. The threshold rate of change may vary based on the final panel temperature <NUM>. For example, at a final panel temperature of <NUM>, the threshold rate of change may be set to +<NUM>/min. At a final panel temperature of <NUM>, the threshold rate of change may be set to +<NUM>/min. Thus, as the final panel temperature <NUM> rises, approaching the threshold panel temperature, the threshold rate of change may decrease.

Based on determining that the final panel temperature <NUM> exceeds the threshold panel temperature, that the temperature rate of change <NUM> exceeds the threshold temperature rate of change, or both, the panel temperature limiter <NUM> can determine to output a signal adjustment <NUM> to the signal adjuster <NUM>. The signal adjustment can be, for example, a mathematical function to be applied to the audio signal <NUM> in order to generate an adjusted audio signal <NUM>.

The panel temperature limiter <NUM> can be programmed with rules determining the signal adjustment <NUM> for various final panel temperatures <NUM> and temperature rates of change <NUM>. For example, a rule may state that when the final panel temperature <NUM> exceeds the threshold panel temperature, the signal adjustment <NUM> includes a function of reducing the audio signal power by a divisor of two. In another example, a rule may state that when the temperature rate of change <NUM> exceeds the threshold temperature rate of change, the signal adjustment <NUM> includes a function of reducing the audio signal power by a factor of one-third. In another example, a rule may state that when the final panel temperature <NUM> exceeds the threshold panel temperature, the signal adjustment <NUM> includes turning off the audio signal.

In some examples, the panel temperature limiter <NUM> can be programmed to output the signal adjustment <NUM> for a designated period of time. For example, in response to determining that the final panel temperature <NUM> exceeds the threshold panel temperature, the panel temperature limiter <NUM> may determine to output a signal adjustment <NUM> of reducing the audio signal power by one half for a period of time of one minute. In some examples, following the period of time of one minute, the panel temperature limiter <NUM> can automatically remove the signal adjustment <NUM>.

In some examples, the panel temperature limiter <NUM> may output a signal adjustment that applies only to certain frequencies of the audio signal <NUM>. In some examples, the panel temperature limiter <NUM> may output multiple signal adjustments that apply to multiple frequency ranges of the audio signal <NUM>. For example, the panel temperature limiter <NUM> may output a first signal adjustment that applies to a first range of frequencies of the audio signal <NUM>, and a second signal adjustment that applies to a second range of frequencies of the audio signal <NUM>.

In some examples, the panel temperature limiter <NUM> can determine to remove the signal adjustment <NUM>. For example, the panel temperature limiter <NUM> may have previously determined to apply a signal adjustment <NUM> to the audio signal <NUM>. The panel temperature limiter <NUM> can continue to monitor the final panel temperature <NUM> and/or the temperature rate of change <NUM>. When the final panel temperature <NUM>, the temperature rate of change <NUM>, or both, return below the programmed thresholds, the panel temperature limiter <NUM> can determine to remove the previously applied signal adjustment <NUM>.

The signal adjuster <NUM> receives the audio signal <NUM> from the signal generator <NUM>, and the signal adjustment <NUM> from the panel temperature limiter <NUM>. The signal adjuster <NUM> can apply the signal adjustment <NUM> to the audio signal <NUM>. For example, for a signal adjustment of reducing by one-half, the signal adjuster <NUM> can reduce the power of the audio signal <NUM> by one-half. The signal adjuster <NUM> outputs an adjusted audio signal <NUM> to the magnetic coil <NUM>.

In some examples, instead of or in addition to the processor <NUM> applying the signal adjustment <NUM> to the audio signal <NUM>, the processor <NUM> may transmit a command to the amplifier <NUM> to adjust amplification. For example, the processor <NUM> may transmit a command to the amplifier <NUM> to reduce amplification of the analog electrical signal, e.g., by one-half. The amplifier <NUM> can then reduce the amplification of the analog electrical signal for a designated period of time, or until receiving a subsequent command from the processor <NUM> to cease reducing the amplification.

When the power of the audio signal is reduced, the current through the magnetic coil <NUM> is reduced. Due to the current being reduced, the magnetic coil <NUM> may then increase temperature at a slower rate, cease increasing in temperature, or decrease in temperature. Due to thermal communication between the magnetic coil <NUM> and the panel <NUM>, the panel <NUM> may likewise increase temperature at a slower rate, cease increasing in temperature, or decrease in temperature. The processor <NUM> can continue to monitor coil current <NUM> and coil voltage <NUM> in order to re-calculate changes in panel temperature.

<FIG> is a flowchart of an example process <NUM> for monitoring temperature of a panel in a panel audio device. The process <NUM> can be performed, for example, by the electronic control module <NUM>.

Briefly, process <NUM> includes providing a current to a magnetic coil of an actuator to cause vibration of a panel, the magnetic coil being in thermal communication with the panel (<NUM>), receiving, from a plurality of electrical sensors electrically coupled to the magnetic coil, time-varying electrical data for the magnetic coil (<NUM>), based on the time-varying electrical data for the magnetic coil, determining an electrical energy provided to the magnetic coil between a first time and a second time (<NUM>), accessing a thermal model of the panel (<NUM>), based on the electrical energy provided to the magnetic coil, and the thermal model of the panel, determining a change in a panel temperature between the first time and the second time (<NUM>), determining a first panel temperature at the first time (<NUM>), based on the first panel temperature, and the change in the panel temperature between the first time and the second time, determining a second panel temperature at the second time (<NUM>), and based on the second panel temperature, adjusting the current provided to the magnetic coil (<NUM>).

In additional detail, the process <NUM> includes providing a current to a magnetic coil of an actuator to cause vibration of a panel, the magnetic coil being in thermal communication with the panel (<NUM>). For example, the magnetic coil can be attached to a surface of the panel such that when a temperature of the magnetic coil rises, the panel temperature likely also rises.

The process <NUM> includes receiving, from a plurality of electrical sensors electrically coupled to the magnetic coil, time-varying electrical data for the magnetic coil (<NUM>). For example, the time-varying electrical data can include a time-varying current through the magnetic coil, and a time-varying voltage across the magnetic coil.

The process <NUM> includes, based on the time-varying electrical data for the magnetic coil, determining an electrical energy provided to the magnetic coil between a first time and a second time (<NUM>). The first time may be, for example, a time of zero seconds. The second time may be, for example, a time of sixty seconds. Based on the current data and the voltage data for the magnetic coil, the electronic control module can determine a time-varying power supplied to the magnetic coil. For example, the time-varying power can include a steady power of 10W supplied to the magnetic coil for a duration of sixty seconds. Based on the power, the electronic control module can determine the electrical energy provided to the magnetic coil. For example, based on the power of 10W over sixty seconds, the electronic control module can determine an electrical energy of <NUM> Joules.

The process <NUM> includes accessing a thermal model of the panel (<NUM>). For example, the thermal model of the panel may accessed from a memory of the electronic control module. The thermal model of the panel may include an association curve between the energy provided to the magnetic coil and the change in panel temperature. The thermal model of the panel may include data representing heat transfer from the magnetic coil to the panel, and from the panel to ambient. The thermal model of the panel can be generated using, for example, mathematical calculations, experimental results, or both. The thermal model of the panel may be generated prior to operation, during a calibration phase, during operation, or a combination of these.

The process <NUM> includes, based on the electrical energy provided to the magnetic coil, and the thermal model of the panel, determining a change in a panel temperature between the first time and the second time (<NUM>). For example, based on the electrical energy of <NUM> Joules, and the thermal model of the panel associating the energy to the change in temperature, the electronic control module may determine a change in a panel temperature of +<NUM> between zero seconds and sixty seconds.

The process <NUM> includes determining a first panel temperature at the first time (<NUM>). The first panel temperature may be stored in the memory of the electronic control module. The first panel temperature may be based on a measurement taken while a pilot tone is applied to the magnetic coil. The first panel temperature may be, for example, <NUM>.

The process <NUM> includes, based on the first panel temperature, and the change in the panel temperature between the first time and the second time, determining a second panel temperature at the second time (<NUM>). For example, based on the first panel temperature of <NUM>, and the change in panel temperature of + <NUM>, the electronic control module can determine a second panel temperature of <NUM>.

The process <NUM> includes, based on the second panel temperature, adjusting the current provided to the magnetic coil (<NUM>). For example, the electronic control module can compare the second panel temperature to a threshold panel temperature. The threshold panel temperature may be, for example, <NUM>. The electronic control module may determine that the second panel temperature of <NUM> exceeds the threshold panel temperature of <NUM>. In response to determining that the second panel temperature exceeds the threshold panel temperature, the electronic control module can determine to adjust the current provided to the magnetic coil. For example, the electronic control module may determine to adjust the current by reducing the current, for example, by a factor of one-half or one-third.

Referring to <FIG>, an exemplary electronic control module <NUM> of a mobile device, such as mobile device <NUM>, includes a processor <NUM>, memory <NUM>, a display driver <NUM>, a signal generator <NUM>, an input/output (I/O) module <NUM>, and a network/communications module <NUM>. These components are in electrical communication with one another (e.g., via a signal bus <NUM>) and with the actuator module <NUM>.

The processor <NUM> may be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions. For example, the processor <NUM> can be a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), or combinations of such devices.

The memory <NUM> has various instructions, computer programs or other data stored thereon. The instructions or computer programs may be configured to perform one or more of the operations or functions described with respect to the mobile device. For example, the instructions may be configured to control or coordinate the operation of the device's display via the display driver <NUM>, the signal generator <NUM>, one or more components of the I/O module <NUM>, one or more communication channels accessible via network/communications module <NUM>, one or more sensors (e.g., biometric sensors, temperature sensors, accelerometers, optical sensors, barometric sensors, moisture sensors and so on), and/or the actuator module <NUM>.

The signal generator <NUM> is configured to produce AC waveforms of varying amplitudes, frequency, and/or pulse profiles suitable for the actuator module <NUM> and producing acoustic and/or haptic responses via the actuator. Although depicted as a separate component, in some embodiments, the signal generator <NUM> can be part of the processor <NUM>. In some embodiments, the signal generator <NUM> can include an amplifier, e.g., as an integral or separate component thereof.

The memory <NUM> can store electrical data that can be used by the mobile device. For example, the memory <NUM> can store electrical data or content such as, for example, audio and video files, documents and applications, device settings and user preferences, timing and control signals or data for the various modules, data structures or databases, and so on. The memory <NUM> may also store instructions for recreating the various types of waveforms that may be used by the signal generator <NUM> to generate signals for the actuator module <NUM>. The memory <NUM> may be any type of memory such as, for example, random access memory, read-only memory, Flash memory, removable memory, or other types of storage elements, or combinations of such devices.

As briefly discussed above, the electronic control module <NUM> may include various input and output components represented in <FIG> as I/O module <NUM>. Although the components of I/O module <NUM> are represented as a single item in <FIG>, the mobile device may include a number of different input components, including buttons, microphones, switches, and dials for accepting user input. In some embodiments, the components of the I/O module <NUM> may include one or more touch sensor and/or force sensors. For example, the mobile device's display may include one or more touch sensors and/or one or more force sensors that enable a user to provide input to the mobile device.

Each of the components of the I/O module <NUM> may include specialized circuitry for generating signals or data. In some cases, the components may produce or provide feedback for application-specific input that corresponds to a prompt or user interface object presented on the display.

As noted above, the network/communications module <NUM> includes one or more communication channels. These communication channels can include one or more wireless interfaces that provide communications between the processor <NUM> and an external device or other electronic device. In general, the communication channels may be configured to transmit and receive data and/or signals that may be interpreted by instructions executed on the processor <NUM>. In some cases, the external device is part of an external communication network that is configured to exchange data with other devices. Generally, the wireless interface may include, without limitation, radio frequency, optical, acoustic, and/or magnetic signals and may be configured to operate over a wireless interface or protocol. Example wireless interfaces include radio frequency cellular interfaces, fiber optic interfaces, acoustic interfaces, Bluetooth interfaces, Near Field Communication interfaces, infrared interfaces, USB interfaces, Wi-Fi interfaces, TCP/IP interfaces, network communications interfaces, or any conventional communication interfaces.

In some implementations, one or more of the communication channels of the network/communications module <NUM> may include a wireless communication channel between the mobile device and another device, such as another mobile phone, tablet, computer, or the like. In some cases, output, audio output, haptic output or visual display elements may be transmitted directly to the other device for output. For example, an audible alert or visual warning may be transmitted from the mobile device <NUM> to a mobile phone for output on that device and vice versa. Similarly, the network/communications module <NUM> may be configured to receive input provided on another device to control the mobile device. For example, an audible alert, visual notification, or haptic alert (or instructions therefore) may be transmitted from the external device to the mobile device for presentation.

Claim 1:
A panel audio loudspeaker, comprising:
a panel (<NUM>);
an actuator (<NUM>) attached to a surface of the panel and configured to cause vibration of the panel, the actuator comprising a magnetic coil (<NUM>) in thermal communication with the panel;
a plurality of electrical sensors (<NUM>, <NUM>) electrically coupled to the magnetic coil and configured to output time-varying electrical data for the magnetic coil; and
an electronic control module (<NUM>) in communication with the magnetic coil and the plurality of electrical sensors, wherein the electronic control module is configured to perform operations comprising:
providing a current to the magnetic coil;
receiving, from the plurality of electrical sensors, the time-varying electrical data (<NUM>, <NUM>) for the magnetic coil;
based on the time-varying electrical data for the magnetic coil, determining an electrical energy (<NUM>) provided to the magnetic coil between a first time and a second time;
accessing a thermal model (<NUM>, <NUM>) of the panel; and
based on the electrical energy provided to the magnetic coil, and the thermal model of the panel, determining a change (<NUM>) in a panel temperature between the first time and the second time.