CN118591424A - Detection and prevention of nonlinear deviations in haptic actuators - Google Patents

Abstract

A method for determining and mitigating over-excursion of an internal mass of an electromechanical transducer may include measuring a sense signal associated with an electromechanical transducer in response to a drive signal driven to the electromechanical transducer, determining a nonlinearity value based on the sense signal, mapping the nonlinearity value to a probability of over-excursion of the internal mass, and applying a gain to a signal path configured to generate the drive signal based on the probability.

Description

Detection and prevention of nonlinear deviations in haptic actuators

Technical Field

The present disclosure generally relates to methods, apparatus, or implementations for haptic devices. In particular, embodiments described herein may disclose systems and methods for detecting and preventing nonlinear excursions in haptic actuators.

Background Art

Vibrotactile transducers, such as linear resonant actuators (LRA), are widely used in portable devices such as mobile phones to generate vibration feedback to users. Various forms of vibrotactile feedback create different touch sensations on the user's skin and can play an increasingly important role in human-computer interaction in modern devices.

LRA can be modeled as a mass-spring electromechanical vibration system. When driven with a properly designed or controlled drive signal, LRA can generate certain desired forms of vibration. For example, a sharp and clear vibration pattern on a user's finger can be used to create a feeling that simulates the click of a mechanical button. This clear vibration can then be used as a virtual switch to replace a mechanical button.

FIG. 1 shows an example of a vibrotactile system in a device 100. The device 100 may include a controller 101 configured to control a signal applied to an amplifier 102. The amplifier 102 may then drive a vibroactuator (e.g., a tactile transducer) 103 based on the signal. The controller 101 may be triggered by a trigger to output a signal. The trigger may, for example, include a pressure or force sensor on a screen or virtual button of the device 100.

Among various forms of vibro-tactile feedback, tonal vibrations of duration can play an important role in notifying the user of the device of certain predetermined events, such as incoming calls or messages, emergency alerts, and timer warnings, etc. In order to effectively generate tonal vibration notifications, it may be desirable to operate the tactile actuator at or near its resonant frequency.

The resonant frequency _f0 of the tactile transducer can be approximately estimated as:

Where C is the compliance of the spring system and M is the equivalent moving mass, which can be determined based on the actual moving parts in the tactile transducer and the mass of the portable device holding the tactile transducer.

The vibration resonance of a tactile transducer may vary over time due to sample-to-sample variations of individual tactile transducers, mobile device component variations, temporal component variations due to aging, and usage conditions such as the varying strength with which a user grips the device.

FIG2 shows an example of a linear resonant actuator (LRA) modeled as a linear system. The LRA is a nonlinear component whose behavior may vary depending on the applied voltage level, operating temperature, and frequency content of the drive signal. However, under certain conditions, these components can be modeled as linear components. In this example, the LRA is modeled as a third-order system with electrical and mechanical elements. In particular, Re and Le are the DC resistance and coil inductance of the coil-magnet system, respectively; and Bl is the magnetic coefficient of the coil. The drive amplifier outputs a voltage waveform V(t) with an output impedance Ro. The terminal voltage _VT (t) can be sensed across the terminals of the tactile transducer. The mass-spring system 201 moves at a velocity u(t).

The tactile system may require precise control of the movement of the tactile transducer. This control may rely on the magnetic coefficient Bl, which may also be referred to as the electromagnetic transfer function of the tactile transducer. In an ideal case, the magnetic coefficient Bl can be given by the product B·l, where B is the magnetic flux density and l is the total length of the electrical conductor within the magnetic field that produces the magnetic flux density B. In the ideal case where motion occurs along a single axis, the magnetic flux density B and the length l should remain constant.

As mentioned above, when current passes through the coil of the electromagnet, the electromagnet is subjected to force due to the interaction between the electromagnet and the permanent magnet. The vibration actuator 103 can be mechanically mounted on the structure of the device 100 so that the vibration caused by the moving mass is transmitted to the device, thereby being felt by the user. In most portable electronic devices, the vibration actuator 103 is driven by a low output impedance amplifier 102 with a voltage waveform. However, due to the acceleration of the mass in the vibration actuator 103, the user may experience a tactile event, which interacts with the rest of the device 100 and the user's hand.

For a given steady-state input voltage signal, the response of an LRA may become increasingly nonlinear as the voltage amplitude increases beyond a certain limit (usually specified by the LRA manufacturer as a maximum voltage level). This nonlinearity is typically caused by amplitude-dependent changes in the spring constant associated with the springs that suspend the LRA's internal mass. This amplitude dependency is typically most prominent at higher voltage levels. Depending on the LRA's construction, a sufficiently large input signal driven at or near the resonant frequency may displace the LRA's internal mass to the point where it contacts the LRA's housing or its mechanical end stops. This behavior is typically referred to as over-excursion. This condition may negatively impact the user experience and, in some cases, cause physical damage to the LRA. Therefore, systems and methods for detecting and preventing such over-excursion may be needed.

Summary of the invention

According to the teachings of the present disclosure, disadvantages and problems associated with existing methods for generating tactile waveforms for electromagnetic transducers may be reduced or eliminated.

According to an embodiment of the present disclosure, a method for determining and mitigating over-excursion of an internal mass of an electromechanical transducer may include measuring a sense signal associated with an electromechanical transducer in response to a drive signal driven to the electromechanical transducer, determining a nonlinearity value based on the sense signal, mapping the nonlinearity value to a probability of over-excursion of the internal mass, and applying a gain to a signal path configured to generate the drive signal based on the probability.

According to these and other embodiments of the present disclosure, a system for determining and mitigating over-excursion of an internal mass of an electromechanical transducer may include an input configured to measure a sensed signal associated with the electromechanical transducer in response to a drive signal driven to the electromechanical transducer, and a nonlinear offset detector configured to determine a nonlinearity value based on the sensed signal, map the nonlinearity value to a probability of over-excursion of the internal mass, and apply a gain to a signal path configured to generate the drive signal based on the probability.

The technical advantages of the present disclosure will be apparent to those skilled in the art from the drawings, descriptions and claims included herein. The objects and advantages of the embodiments will be realized and accomplished at least by the elements, features and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the present disclosure, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and their advantages may be obtained by referring to the following description taken in conjunction with the accompanying drawings, wherein like reference numerals indicate like features, and wherein:

FIG1 shows an example of a vibrotactile system in a device known in the art;

FIG2 shows an example of a linear resonant actuator (LRA) modeled as a linear system as known in the art;

FIG3 illustrates selected components of an example host device according to an embodiment of the present disclosure;

FIG4 illustrates a cross-sectional view of an example electromagnetic load implemented as a tactile transducer according to an embodiment of the present disclosure; and

5 illustrates a graph of an example gain that a waveform pre-processor may apply to a raw transducer drive signal as a function of an over-excursion probability to generate a processed transducer drive signal in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

The following description sets forth example embodiments according to the present disclosure. Further example embodiments and implementations will be apparent to those of ordinary skill in the art. In addition, those of ordinary skill in the art will recognize that various equivalent techniques may be applied to replace or combine the embodiments discussed below, and all such equivalent techniques shall be deemed to be included in the present disclosure.

Various electronic devices or smart devices may have transducers, speakers, and acoustic output transducers, such as any transducer for converting a suitable electrical drive signal into an acoustic output (such as an acoustic pressure wave or a mechanical vibration). For example, many electronic devices may include one or more speakers or loudspeakers for sound generation, such as for playback of audio content, voice communication, and/or for providing audible notifications.

Such a speaker or microphone may include an electromagnetic actuator, such as a voice coil motor, which is mechanically coupled to a flexible diaphragm (such as a traditional microphone cone), or which is mechanically coupled to a surface of the device (such as a glass screen of a mobile device). Some electronic devices may also include an acoustic output transducer capable of generating ultrasonic waves, such as for proximity detection applications and/or machine-to-machine communications.

Many electronic devices may additionally or alternatively include more specialized acoustic output transducers, such as tactile transducers, which are customized to generate vibrations for tactile control feedback or notification to a user. Additionally or alternatively, the electronic device may have a connector (e.g., a socket) for removable mating connection with a corresponding connector of an accessory device, and may be arranged to provide a drive signal to the connector to drive one or more types of transducers of the above-mentioned accessory device when connected. Such an electronic device will therefore include a drive circuit for driving the transducer of the host device or connected accessory with a suitable drive signal. For acoustic or tactile transducers, the drive signal may typically be an analog time-varying voltage signal, such as a time-varying waveform.

3 illustrates selected components of an example host device 300 in accordance with an embodiment of the present disclosure that incorporates force sensing using an electromagnetic load 301 in the host device 300. The host device 300 may include, but is not limited to, a mobile device, a home application, a vehicle, and/or any other system, device, or apparatus including a human-machine interface. The electromagnetic load 301 may include any suitable load having a complex impedance, including but not limited to a tactile transducer, a speaker, a micro speaker, a piezoelectric transducer, or other suitable transducer.

Turning briefly to FIG. 4 , FIG. 4 illustrates a cross-sectional view of an example electromagnetic load 301 implemented as a tactile transducer according to an embodiment of the present disclosure. As shown in FIG. 4 , the electromagnetic load 301 may include a moving mass 402 mechanically coupled to a housing 404 via one or more springs 406. The moving mass 402 may include a ferromagnetic material such that an alternating current flowing in a coil 408 surrounding the moving mass 402 may induce an alternating mechanical field that causes the moving mass 402 to vibrate (e.g., up and down in the directions shown in FIG. 4 ). The housing 404 may include an end stop 410 configured to engage with a corresponding feature 412 of the moving mass 402 so as to limit the excursion of the moving mass 402 within the housing 404. As described above, the mechanical contact between the feature 412 and the end stop 410 may result in a nonlinearity between the electromagnetic signal driving the electromagnetic load 301 and the displacement or excursion of the moving mass 402 relative to the housing 404.

3 , in operation, the signal generator 324 of the processing subsystem 305 of the host device 300 may generate a raw transducer drive signal x′(t) (which may be a waveform signal, such as a tactile waveform signal or an audio signal, in some embodiments). The raw transducer drive signal x′(t) may be generated based on the desired playback waveform received by the signal generator 324.

The raw transducer drive signal x′(t) may be received by a waveform preprocessor 326, as described in more detail below, which may optimize the raw transducer drive information x′(t) based on the probability of over-excursion of the moving mass of the electromagnetic load 301 to generate a processed transducer drive signal x(t), as described in more detail below.

The processed transducer drive signal x(t) may then be amplified by an amplifier 306 to generate a drive signal V(t) for driving the electromagnetic load 301. In response to the drive signal V(t), a sense terminal voltage _VT (t) of the electromagnetic load 301 may be sensed by a terminal voltage sensing block 307 (e.g., a voltmeter) and converted to a digital representation by a first analog-to-digital converter (ADC) 303. Similarly, a sense current I(t) may be converted to a digital representation by a second ADC 304. The current I(t) may be sensed across a shunt resistor 302 having a resistance _Rs coupled to the terminals of the electromagnetic load 301.

As shown in FIG. 3 , the processing subsystem 305 may include a nonlinear offset detector 308 configured to determine whether there is nonlinearity between the electromagnetic signal driving the electromagnetic load 301 and the displacement of a moving mass (e.g., the moving mass 402) of the electromagnetic load 301 based on the sensed terminal voltage _VT (t) and the sensed current I(t), and determine a probability P of excessive offset of the moving mass based on such nonlinearity.

To illustrate this functionality of the nonlinear offset detector 308, the nonlinear offset detector 308 may estimate the back EMF voltage _VB (t) of the electromagnetic load 301. In general, the back EMF voltage _VB (t) may not be directly measured from outside the tactile transducer. However, the terminal voltage _VT (t) measured at the tactile transducer terminals may have the following relationship to _VB (t):

where the parameters are defined as described with reference to Figure 2. Therefore, the back EMF voltage _VB (t) can be estimated according to equation (2), which can be rearranged as:

The back EMF voltage _VB (t) can in turn provide an estimate of the velocity of the moving mass of the electromagnetic load 301 because the back EMF voltage _VB (t) can be proportional to such velocity. Thus, the back EMF voltage _VB (t) can be estimated based on an equivalent electrical model of the electromagnetic load 301, and such an electrical model can vary depending on the parameters of the electromagnetic load 301 and the host device 300, including the resonant frequency and the quality factor.

The estimates of the DC resistance Re and inductance Le may not need to be accurate (e.g., within an error range of about 10% is acceptable), and therefore, offline calibration or fixed values in the data sheet specification may be sufficient. For example, in some embodiments, the nonlinear offset detector 308 can determine the estimated back EMF voltage _VB (t) according to the teachings of U.S. patent application Ser. No. 16/559,238 filed on Sep. 3, 2019, the entire contents of which are incorporated herein by reference.

By measuring both the sense current I(t) and the back EMF voltage _VB (t), the nonlinear offset detector 308 can estimate the internal state of the electromagnetic load 301. Distortion and other nonlinearities can be extracted from the sense current I(t), the back EMF voltage _VB (t), or a combination of both. Based on the amount of nonlinearity observed relative to a threshold, the nonlinear offset detector 308 can control the processed transducer drive signal x(t) to prevent excessive offset.

4 , if the spring 406 of the electromagnetic load 301 is overstretched, the moving mass 402 may exhibit nonlinear behavior to the processed sensor drive signal x(t). In addition, the collision between the moving mass 402 and the end stop 410 may also cause nonlinear distortion. Therefore, these two situations can define a nonlinear behavior region where the electromagnetic load 301 is more likely to be over-deflected.

To determine the likelihood or probability of an over-excursion, nonlinear excursion detector 308 may use electrical measurements (eg, terminal voltage _VT (t), sense current I(t), back EMF voltage _VB (t)) to determine the occurrence of nonlinearity.

For example, when the processed transducer drive signal x(t) is non-periodic, as is the case with haptic playback waveforms during operation of the host device 300, the probability P of over-excursion can be determined by comparing a voltage content ratio associated with the terminal voltage _VT (t) and a current-to-voltage ratio associated with the sense current I(t). The voltage content ratio can include a ratio of high-frequency content present in the terminal voltage _VT (t) above a specific frequency to low-frequency content present in the terminal voltage _VT (t) below a specific frequency. Similarly, the current content ratio can include a ratio of high-frequency content present in the sense current I(t) above a specific frequency to low-frequency content present in the sense current I(t) below a specific frequency. The mathematical difference or ratio between the current content ratio and the voltage content ratio can represent the probability P of over-excursion.

In addition to or instead of comparing the current content ratio to the voltage content ratio, the nonlinear excursion detector 308 may determine the probability P of an over-excursion based on whether a noise gate for the magnitude of the sense current I(t) is triggered while a noise gate for the magnitude of the terminal voltage _VT (t) is not triggered.

As another example, in an offline process where no haptic waveform is generated, signal generator 324 can generate a raw transducer drive signal x'(t), a pilot tone above the resonant frequency of electromagnetic load 301, and nonlinear excursion detector 308 can measure the total harmonic distortion (THD) of the pilot tone caused by electromagnetic load 301 entering a nonlinear behavior region based on sensed current I(t) and terminal voltage _VT (t). Such THD can be calculated as a function of the pilot tone and its harmonics. Nonlinear excursion detector 308 can also map the measured THD to a probability of excessive excursion at a particular frequency and/or amplitude, which waveform preprocessor 326 can use to generate a processed transducer drive signal x(t).

The waveform processor 326 may receive a signal indicating a probability P of over-excursion and based thereon modify the raw transducer drive signal x′(t) (e.g., by applying an appropriate gain and/or filter response) to generate a processed transducer drive signal x(t) such that the likelihood of over-excursion of the moving mass of the electromagnetic transducer 301 is reduced from the probability P determined by the nonlinear excursion detector 308 so as to eliminate or reduce the occurrence of the moving mass 402 exceeding a rated excursion limit and/or other operating limits (e.g., limits defined by the manufacturer of the electromagnetic load). For example, FIG. 5 shows a graph of an example gain that the waveform pre-processor 326 may apply to the raw transducer drive signal x′(t) as a function of the probability P of over-excursion in order to generate a processed transducer drive signal x(t) in accordance with an embodiment of the present disclosure.

Based on the above, a system and method for determining and mitigating excessive excursion of an internal mass (e.g., moving mass 402) and/or other electromagnetic load (e.g., electromagnetic load 301) of a tactile actuator can be provided, wherein a nonlinear value of the electromagnetic load can be measured based on at least a current signal (e.g., sensed current I(t)) associated with the electromagnetic load. The nonlinear value can be mapped to a likelihood value (e.g., probability P) of excessive excursion of the moving mass. In addition, the likelihood value can be used to determine a gain reduction applied to a transducer drive signal.

As used herein, when two or more elements are referred to as being “coupled” to each other, the term indicates that the two or more elements are in electronic or mechanical communication, as applicable, whether indirectly or directly, with or without intervening elements.

The present disclosure covers all changes, substitutions, variations, alterations and modifications to the example embodiments herein that will be understood by a person of ordinary skill in the art. Similarly, where appropriate, the appended claims cover all changes, substitutions, variations, alterations and modifications to the example embodiments herein that will be understood by a person of ordinary skill in the art. In addition, in the appended claims, references to a device or system or a component of a device or system adapted to, arranged to, capable of, configured to, enabled to, operable to, or operable to perform a specific function cover the device, system or component, regardless of whether it or the specific function is activated, turned on or unlocked, as long as the device, system or component is so adapted, arranged, capable of, configured to, enabled to, operable to, or operable to. Therefore, without departing from the scope of the present disclosure, the systems, devices and methods described herein may be modified, added to or omitted. For example, the components of the systems and devices may be integrated or separated. In addition, the operations of the systems and devices disclosed herein may be performed by more, fewer or other components, and the described methods may include more, fewer, or other steps. In addition, the steps may be performed in any suitable order. As used in this document, "each" refers to each member of a set or each member of a subset of a set.

Although exemplary embodiments are shown in the drawings and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should not be limited in any way to the exemplary implementations and techniques shown in the drawings and described above.

Unless specifically noted otherwise, items depicted in the drawings are not necessarily drawn to scale.

All examples and conditional language listed herein are intended for teaching purposes to help readers understand the present disclosure and the concepts contributed by the inventors to further advance the art, and are interpreted as not being limited to these specific examples and conditions. Although the embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions and modifications may be made thereto without departing from the spirit and scope of the present disclosure.

Although specific advantages have been listed above, various embodiments may include some, none, or all of the listed advantages. In addition, other technical advantages may become apparent to those of ordinary skill in the art after reviewing the above drawings and descriptions.

To assist the Patent Office and any reader of any patent issuing from this application in understanding the claims appended hereto, applicants wish to note that unless the phrase "means for" or "step for" is expressly used in a particular claim, they do not intend for any of the appended claims or claim elements to invoke 35 U.S.C. §112(f).

Claims (20)

1. A method for determining and mitigating excessive deflection of an internal mass of an electromechanical transducer, the method comprising: measuring a sense signal associated with the electromechanical transducer in response to a drive signal driven to the electromechanical transducer; determining a nonlinearity value based on the sensed signal; mapping the nonlinearity value to a probability of over-excursion of the inner mass; and A gain is applied to a signal path configured to generate the drive signal based on the probability. 2 . The method of claim 1 , wherein determining the nonlinear value based on the sensed signal comprises determining a back electromotive force associated with the electromechanical transducer based on the sensed signal. 3. The method of claim 1 , wherein determining the nonlinearity value comprises: determining a first content ratio, the first content ratio being equal to a ratio of content present in the drive signal in a first frequency band to content present in the drive signal in a second frequency band; determining a second content ratio, the second content ratio being equal to a ratio of content present in the sensing signal in the first frequency band to content present in the second frequency band; and The non-linear value is determined based on a comparison of the first content ratio and the second content ratio. 4. The method of claim 1 , wherein determining the nonlinearity value comprises: determining a first content ratio, the first content ratio being equal to a ratio of high frequency content present in the drive signal above a particular frequency to low frequency content present in the drive signal below the particular frequency; determining a second content ratio, the second content ratio being equal to a ratio of high frequency content present in the sensing signal above the specific frequency to low frequency content present in the sensing signal below the specific frequency; and The non-linear value is determined based on a comparison of the first content ratio and the second content ratio. 5 . The method of claim 1 , wherein determining the nonlinearity value comprises determining the nonlinearity value based on noise gating of an amplitude of the drive signal compared to noise gating of an amplitude of the sense signal. 6. The method of claim 1 , wherein determining the nonlinearity value comprises: generating the drive signal as a pilot tone at a frequency higher than a resonant frequency of the electromechanical transducer; measuring total harmonic distortion present in the sense signal in response to the pilot tone; and The nonlinearity value is determined based on the total harmonic distortion. 7. The method according to claim 1, wherein: Determining the nonlinearity value based on the sensed signal comprises measuring a harmonic component of the sensed signal; and The method also includes determining an orientation of the electromagnetic transducer based on an amplitude and a phase of a harmonic component of the sense signal. 8. The method of any one of claims 1 to 7, further comprising attenuating the drive signal based on the gain. 9. The method according to any one of claims 1 to 8, wherein: The driving signal is a voltage signal; and The sensing signal is a current signal. 10. The method of any one of claims 1 to 9, wherein the electromagnetic transducer is one of a tactile transducer, a voice coil, and a speaker. 11. A system for determining and mitigating excessive deflection of an internal mass of an electromechanical transducer, the system comprising: an input configured to measure a sense signal associated with the electromechanical transducer in response to a drive signal driven to the electromechanical transducer; and A non-linear offset detector, the non-linear offset detector being configured to: determining a nonlinearity value based on the sensed signal; mapping the nonlinearity value to a probability of over-excursion of the inner mass; and A gain is applied to a signal path configured to generate the drive signal based on the probability. 12 . The system of claim 11 , wherein determining the nonlinear value based on the sensed signal comprises determining a back electromotive force associated with the electromechanical transducer based on the sensed signal. 13. The system of claim 11, wherein determining the nonlinearity value comprises: determining a first content ratio, the first content ratio being equal to a ratio of content present in the drive signal in a first frequency band to content present in the drive signal in a second frequency band; determining a second content ratio, the second content ratio being equal to a ratio of content present in the sensing signal in the first frequency band to content present in the second frequency band; and The non-linear value is determined based on a comparison of the first content ratio and the second content ratio. 14. The system of claim 11, wherein determining the nonlinearity value comprises: determining a first content ratio, the first content ratio being equal to a ratio of high frequency content present in the drive signal above a particular frequency to low frequency content present in the drive signal below the particular frequency; determining a second content ratio, the second content ratio being equal to a ratio of high frequency content present in the sensing signal above the specific frequency to low frequency content present in the sensing signal below the specific frequency; and The non-linear value is determined based on a comparison of the first content ratio and the second content ratio. 15 . The system of claim 11 , wherein determining the nonlinearity value comprises determining the nonlinearity value based on noise gating of an amplitude of the drive signal compared to noise gating of an amplitude of the sense signal. 16. The system of claim 11, wherein determining the nonlinearity value comprises: generating the drive signal as a pilot tone at a frequency higher than a resonant frequency of the electromechanical transducer; measuring total harmonic distortion present in the sense signal in response to the pilot tone; and The nonlinearity value is determined based on the total harmonic distortion. 17. The system of claim 11, wherein: Determining the nonlinearity value based on the sensed signal comprises measuring a harmonic component of the sensed signal; and The method also includes determining an orientation of the electromagnetic transducer based on an amplitude and a phase of a harmonic component of the sense signal. 18. The system of any one of claims 11 to 17, wherein the non-linear offset detector is further configured to attenuate the drive signal based on the gain. 19. A system according to any one of claims 11 to 18, wherein: The driving signal is a voltage signal; and The sensing signal is a current signal. 20. The system of any one of claims 11 to 19, wherein the electromagnetic transducer is one of a tactile transducer, a voice coil, and a speaker.