Detecting and preventing nonlinear bias in haptic actuators.

Abstract

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

Description

[Technical field]

[0001] The present disclosure generally relates to methods, apparatus, or implementations relating to haptic devices. In particular, embodiments described herein may disclose systems and methods for detecting and preventing non-linear excursions in haptic actuators. [Background technology]

[0002] Vibrotactile transducers, such as linear resonant actuators (LRAs), are widely used in portable devices such as mobile phones to generate vibration feedback to users. Various forms of vibrotactile feedback can generate different touch sensations on the user's skin and play an increasing role in human-machine interaction in modern devices.

[0003] An LRA can be modeled as a mass-spring electromechanical vibration system. When driven with a properly designed or controlled drive signal, the LRA can generate a particular desired form of vibration. For example, a sharp, well-defined vibration pattern to a user's finger can be used to create a sensation that mimics the click of a mechanical button. This well-defined vibration can then be used as a virtual switch to replace the mechanical button.

[0004] 1 shows an example of a vibrotactile system of 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 vibration actuator (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 include, for example, a pressure or force sensor on a screen or a virtual button of the device 100.

[0005] Among the various forms of vibrotactile feedback, sound vibrations of a certain duration can play an important role in notifying a device user of certain predefined events such as incoming calls or messages, emergency alerts, timer warnings, etc. To efficiently generate sound vibration notifications, it may be desirable to operate the haptic actuator at or near the resonant frequency of the haptic actuator.

[0006] The resonant frequency f0 of a tactile transducer can be roughly estimated by the following equation:

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[0007] The vibration resonance of a tactile transducer can change from one sample to another due to variations between individual tactile transducer samples, variations in handheld device assemblies, changes in components over time due to aging, and different usage conditions, such as how tightly a user grips the device.

[0008] FIG. 2 shows an example of a linear resonant actuator (LRA) modeled as a linear system. The LRA is a nonlinear component that may behave differently depending on, for example, the applied voltage level, the operating temperature, and the frequency content of the drive signal. However, these components can be modeled as linear components within certain conditions. The LRA is modeled as a third-order system with electrical and mechanical elements in this example. Re and Le are the DC resistance and coil inductance of the coil-magnet system, respectively, and Bl is the magnetic force coefficient of the coil. The drive amplifier outputs a voltage waveform V(t) with an output impedance Ro. The terminal voltage V T(t) can be sensed across the terminals of a tactile transducer. The mass-spring system 201 moves with a velocity u(t).

[0009] Haptic systems may require precise control of the motion of a tactile transducer. Such control may depend on the magnetic force coefficient Bl, which may also be known as the electromagnetic transfer function of the tactile transducer. The magnetic force coefficient Bl, in the ideal case, is given by the product B·l, where B is the magnetic flux density and l is the total length of the conductor in the magnetic field that produces the flux density B. In the ideal case where the motion occurs along a single axis, both the magnetic flux density B and the length l should remain constant.

[0010] As explained above, when a current is passed through the coil of the electromagnet, a force may be applied to the electromagnet due to the interaction between the electromagnet and the permanent magnet. The vibration actuator 103 may be mechanically attached to the structure of the device 100 such that vibrations due to the moving mass are transferred to the device and can be felt by the user. In most portable electronic devices, the vibration actuator 103 is driven by a voltage waveform from a low output impedance amplifier 102. However, the user may experience a haptic event due to the mass accelerating within the vibration actuator 103 and acting against the mass of the rest of the device 100 as well as the user's hand.

[0011] Given a steady input voltage signal, the response of an LRA can become increasingly nonlinear as the amplitude of the voltage increases beyond a certain limit, which is typically specified by the LRA manufacturer as a maximum voltage level. This nonlinearity is typically caused by the change in spring constant associated with the springs that suspend the LRA's internal mass as a function of amplitude. Such amplitude dependence is typically most pronounced at higher voltage levels. Depending on the construction of the LRA, a sufficiently large input signal driven at or near its resonant frequency may displace the LRA's internal mass to such an extent that it contacts the LRA's housing or a mechanical end stop on the housing. Such behavior is typically referred to as over-excursion. Such an event can adversely affect the user experience and, in some cases, physically damage the LRA. Thus, systems and methods for detecting and protecting against such over-excursion may be desirable. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] U.S. Patent Application Serial No. 16 / 559,238 Summary of the Invention [Means for solving the problem]

[0013] In accordance with the teachings of the present disclosure, drawbacks and problems associated with existing approaches to generating haptic waveforms from electromagnetic transducers may be reduced or eliminated.

[0014] According to an embodiment of the present disclosure, a method for determining and reducing an excessive deflection of an internal mass of an electromechanical transducer may include measuring a sense signal associated with the electromechanical transducer in response to a drive signal applied to the electromechanical transducer, determining a nonlinearity value based on the sense signal, mapping the nonlinearity value to a probability of excessive deflection of the internal mass, and applying a gain based on the probability to a signal path configured to generate the drive signal.

[0015] According to these and other embodiments of the present disclosure, a system for determining and reducing excess deflection of an internal mass of an electromechanical transducer may include an input configured to measure a sense signal associated with the electromechanical transducer in response to a drive signal applied to the electromechanical transducer, and a nonlinear deflection detector configured to determine a nonlinearity value based on the sense signal, map the nonlinearity value to a probability of excess deflection of the internal mass, and apply a gain based on the probability to a signal path configured to generate the drive signal.

[0016] The technical advantages of the present disclosure will be readily apparent to those skilled in the art from the figures, descriptions, and claims contained herein. The object and advantages of the embodiments will be realized and attained at least by the elements, features, and combinations particularly pointed out in the claims.

[0017] 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 scope of the claims set forth in this disclosure.

[0018] A more complete understanding of the present embodiments and their advantages can be obtained by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals refer to like features and in which: [Brief description of the drawings]

[0019] [Figure 1]FIG. 1 illustrates an example of a vibrotactile system for a device as known in the art. [Diagram 2] FIG. 1 illustrates an example of a linear resonant actuator (LRA) modeled as a linear system, as known in the art. [Diagram 3] FIG. 2 illustrates selected components of an exemplary host device, in accordance with an embodiment of the present disclosure. [Figure 4] 1 is a cross-sectional view of an exemplary electromagnetic load implemented as a tactile transducer according to an embodiment of the present disclosure. [Diagram 5] 11 is a graph of an example gain as a function of probability of over-excursion that a waveform pre-processor can apply to a raw transducer drive signal to generate a processed transducer drive signal in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The following description describes exemplary embodiments according to this disclosure. Further exemplary embodiments and implementations will be apparent to those skilled in the art. Furthermore, those skilled in the art will recognize that various equivalent techniques can be applied in place of or in combination with the embodiments discussed below. All such equivalent techniques are to be considered as being encompassed by this disclosure.

[0021] Various electronic or smart devices can include transducers, speakers, and acoustic output transducers, e.g., any transducer that converts a suitable electrical drive signal into an acoustic output, such as sound pressure waves or mechanical vibrations. For example, many electronic devices can include one or more speakers or loudspeakers for generating sound, e.g., to enable playback of audio content, voice communication, and / or audible notifications.

[0022] Such speakers or loudspeakers may comprise an electromagnetic actuator, e.g., a voice coil motor, that is mechanically coupled to a flexible diaphragm, e.g., a conventional loudspeaker cone, or to a surface of the device, e.g., a glass screen in a mobile device. Some electronic devices may also comprise acoustic output transducers capable of producing ultrasound waves, e.g., for use in proximity detection type applications and / or machine-to-machine communication.

[0023] Many electronic devices may additionally or alternatively comprise more specialized acoustic output transducers, for example tactile transducers adapted to generate vibrations for tactile control feedback or notification to a user. The electronic device may additionally or alternatively comprise a connector, for example a socket, for removably mating 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 of the above-mentioned types of transducers of the accessory device upon connection. Such an electronic device would therefore comprise a drive circuit that drives the transducers of the host device or of the connected accessory with a suitable drive signal. For acoustic or tactile transducers, the drive signal may generally be a time-varying analog voltage signal, for example a time-varying waveform.

[0024] 3 illustrates selected components of an exemplary host device 300 incorporating force sensing using an electromagnetic load 301 of the host device 300 according to an embodiment of the present disclosure. The host device 300 may include, but is not limited to, a portable device, a home application, a vehicle, and / or any other system, device, or apparatus having 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 loudspeaker, a micro-speaker, a piezoelectric transducer, or other suitable transducer.

[0025] Turning briefly to FIG. 4, FIG. 4 illustrates a cross-sectional view of an exemplary electromagnetic load 301 implemented as a tactile transducer according to an embodiment of the present disclosure. The electromagnetic load 301 may comprise a moving mass 402 mechanically coupled to a housing 404 via one or more springs 406 as shown in FIG. 4. The moving mass 402 may comprise a ferromagnetic material such that an alternating current flowing through a coil 408 surrounding the moving mass 402 may induce an alternating mechanical field that causes the moving mass 402 to oscillate (e.g., up and down in the orientation shown in FIG. 4). The housing 404 may comprise an end stop 410 configured to engage a corresponding feature 412 of the moving mass 402 to limit the bias of the moving mass 402 within the housing 404. As discussed above, the mechanical contact between the mechanism 412 and the end stop 410 can cause nonlinearity between the electromagnetic signal driving the electromagnetic load 301 and the displacement or bias of the moving mass 402 relative to the housing 404.

[0026] 3, in operation, the signal generator 324 of the processing subsystem 305 of the host device 300 may generate an unprocessed transducer drive signal x'(t), which in some embodiments may be a waveform signal, such as a haptic waveform signal or an audio signal. The unprocessed transducer drive signal x'(t) may be generated based on a desired playback waveform received by the signal generator 324.

[0027] The waveform pre-processor 326 can receive the raw transducer drive signal x'(t), and the waveform pre-processor 326 can optimize the raw transducer drive signal x'(t) based on the probability of over-excursion of the moving mass of the electromagnetic load 301, as described in more detail below, and generate a processed transducer drive signal x(t), as described in more detail below.

[0028] 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), the sensed terminal voltage V of the electromagnetic load 301 may be T The sensed current I(t) can 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, the sensed current I(t) can be converted to a digital representation by a second ADC 304. The current I(t) is coupled to a resistance R coupled to the terminals of the electromagnetic load 301. s The sensed signal can be sensed across a shunt resistor 302 having a

[0029] As shown in FIG. 3, the processing subsystem 305 detects the sense terminal voltage V T The electromagnetic load 301 may include a nonlinear bias detector 308 configured to determine the presence of nonlinearity between the electromagnetic signal driving the electromagnetic load 301 and the displacement of a moving mass (e.g., moving mass 402) of the electromagnetic load 301 based on the sensed current I(t) and the nonlinearity, and to determine a probability P of over-deflection of the moving mass based on such nonlinearity.

[0030] To explain the function of the nonlinear bias detector 308, the nonlinear bias detector 308 detects the back EMF voltage V of the electromagnetic load 301 as B (t) can be estimated. In general, the back EMF voltage V B (t) cannot be measured directly from the outside of the tactile transducer. However, the terminal voltage V T (t) is V B (t) can be related to

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[0031] The estimates of the DC resistance Re and inductance Le may not need to be precise (e.g., within about 10% error may be acceptable), and thus fixed values ​​from an offline calibration or from a data sheet specification may be sufficient. As an example, the nonlinear bias detector 308 may, in some embodiments, calculate the estimated back EMF voltage V according to the teachings of U.S. patent application Ser. No. 16 / 559,238, filed Sep. 3, 2019. B (t), which is incorporated herein by reference in its entirety.

[0032] The nonlinear bias detector 308 detects the sensed current I(t) and the back EMF voltage V B Using both measurements of the sensed current I(t), the back EMF voltage V, the internal state of the electromagnetic load 301 can be estimated. B (t), or a combination of both. The nonlinearity detector 308 can control the processed transducer drive signal x(t) based on the amount of nonlinearity observed and compared to a threshold to prevent over-excursion.

[0033] 4, the moving mass 402 may exhibit nonlinear behavior with respect to the processed transducer drive signal x(t) if the spring 406 of the electromagnetic load 301 is overstretched. Additionally, a collision between the moving mass 402 and the end stop 410 may also result in nonlinear distortion. From these two scenarios, a region of nonlinear behavior may thus be defined where the electromagnetic load 301 is more likely to be over-exposed.

[0034] The non-linear bias detector 308 detects electrical measurements (e.g., terminal voltage V T (t), sensing current I(t), reverse EMF voltage V B (t)) can be used to determine the occurrence of nonlinearity.

[0035] For example, when the processed transducer drive signal x(t) is non-periodic, as is the case for a haptic playback waveform during operation of the host device 300, the terminal voltage V T By comparing the voltage component ratio associated with the sensed current I(t) to the current-voltage ratio associated with the sensed current I(t), the probability of over-bias P can be determined. The voltage component ratio is expressed as T (t) is the terminal voltage V of the high-frequency component exceeding a specific frequency T The current component ratio may include a ratio of high frequency components above a certain frequency present in the sensed current I(t) to low frequency components below a certain frequency present in the sensed current I(t). The current component ratio may similarly include a ratio of high frequency components above a certain frequency present in the sensed current I(t) to low frequency components below a certain frequency present in the sensed current I(t). The mathematical difference or ratio between the current component ratio and the voltage component ratio may represent the probability P of over-bias.

[0036] In addition to or as an alternative to comparing the ratio of the current components to the ratio of the voltage components, the nonlinear bias detector 308 may also compare the terminal voltage V T The probability P of over-bias may be determined based on whether noise gating is triggered for a magnitude of the sensed current I(t) versus not being triggered for a magnitude of I(t).

[0037] As another example, in an offline process where no haptic waveforms are being generated, the signal generator 324 can generate a pilot tone above the resonant frequency of the electromagnetic load 301 as the raw transducer drive signal x'(t), and the nonlinear bias detector 308 can measure the sensed current I(t) and terminal voltage V T Based on (t), the total harmonic distortion (THD) of the pilot tone caused by the electromagnetic load 301 entering a region of nonlinear behavior can be measured. Such THD can be calculated as a function of the pilot tone and the harmonics of the pilot tone. The nonlinear bias detector 308 can further map the measured THD to a probability of excess bias at a particular frequency and / or amplitude that the waveform pre-processor 326 can use to generate the processed transducer drive signal x(t).

[0038] To prevent or reduce the occurrence of the moving mass 402 exceeding rated deflection limits and / or other operational limits (e.g., limits defined by the electromagnetic load manufacturer), the waveform processor 326 can receive a signal indicative of the probability P of over-deflection and modify the raw transducer drive signal x'(t) (e.g., by applying an appropriate gain and / or filter response) based on the probability P to generate a processed transducer drive signal x(t) such that the likelihood of over-deflection of the moving mass of the electromagnetic transducer 301 is less than the probability P determined by the non-linear deflection detector 308. For example, FIG. 5 illustrates a graph of an example gain as a function of the probability P of over-deflection that the waveform pre-processor 326 can apply to the raw transducer drive signal x'(t) to generate a processed transducer drive signal x(t) in accordance with an embodiment of the present disclosure.

[0039] In accordance with the foregoing, systems and methods can be provided for determining and reducing excess deflection of an internal mass (e.g., moving mass 402) of a haptic actuator and / or other electromagnetic load (e.g., electromagnetic load 301), where a nonlinearity 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 nonlinearity value can be mapped to a likelihood value (e.g., probability P) of excess deflection of the moving mass. Further, the likelihood value can be used to determine an amount of gain attenuation that should be applied to a transducer drive signal.

[0040] As used herein, when two or more elements are referred to as being "coupled" to one another, such term indicates that such two or more elements are in electronic communication or mechanical communication, as appropriate, whether indirectly or directly connected, with or without intervening elements.

[0041] This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that would be understood by a person skilled in the art. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that would be understood by a person skilled in the art. Furthermore, any reference in the appended claims to an apparatus or system, or a part of an apparatus or system, that is adapted, arranged, capable, configured, enabled, operable, or operates to perform a particular function encompasses that apparatus, system, or part, or that particular function is activated, turned on, or unlocked, so long as the apparatus, system, or part is so adapted, arranged, capable, configured, enabled, operable, or operates. Thus, modifications, additions, or omissions can be made to the systems, apparatus, and methods described herein without departing from the scope of the disclosure. For example, the parts of the systems and apparatus may be integrated or separated. Additionally, the operations of the systems and devices disclosed herein may be performed by more, fewer, or other components, and the methods described may include more, fewer, or other steps. Additionally, 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.

[0042] 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, and the present disclosure should in no way be limited to the exemplary implementations and techniques shown in the drawings and described above.

[0043] Unless specifically noted, items illustrated in the drawings are not necessarily drawn to scale.

[0044] All examples and conditional language recited in the specification are intended for educational purposes to aid the reader in understanding the present disclosure and concepts that contribute to the inventors furthering the art, and are not to be construed as limitations on such specifically recited examples and conditions. Although embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations can be made to the embodiments of the present disclosure without departing from the spirit and scope of the present disclosure.

[0045] While certain advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Additionally, other technical advantages may be readily apparent to one of ordinary skill in the art after reviewing the foregoing figures and description.

[0046] Applicant wishes to assist the Patent Office, and any reader of any patent that may issue on this application, in interpreting the claims appended to this specification, that none of the appended claims or claimed elements are intended to invoke 35 U.S.C. 112(f), except to the extent that the words "means for" or "step for" are expressly used in a particular claim.

Claims

1. 1. A method for determining and reducing excess internal mass deflection in an electromechanical transducer, the method comprising: measuring a sense signal associated with the electromechanical transducer in response to a drive signal being applied to the electromechanical transducer; determining a value of nonlinearity based on the sensed signal; mapping the nonlinearity value to a probability of over-excursion of the internal mass; applying a gain to a signal path configured to generate the drive signal based on the probability; A method comprising:

2. The method of claim 1 , wherein determining the value of the nonlinearity based on the sensed signal comprises determining a back electromotive force associated with the electromechanical transducer based on the sensed signal.

3. determining the value of the nonlinearity, determining a first component ratio equal to a ratio of a first frequency band component present in the drive signal to a second frequency band component present in the drive signal; determining a second component ratio equal to a ratio of components in the first frequency band present in the sensed signal to components in the second frequency band; determining a value of the nonlinearity based on a comparison of the first component ratio and the second component ratio; The method of claim 1 , comprising:

4. determining the value of the nonlinearity, determining a first component ratio equal to a ratio of high frequency components present in the drive signal above a particular frequency to low frequency components present in the drive signal below the particular frequency; determining a second component ratio equal to a ratio of high frequency components present in the sensing signal above the particular frequency to low frequency components present in the sensing signal below the particular frequency; determining a value of the nonlinearity based on a comparison of the first component ratio and the second component ratio; The method of claim 1 , comprising:

5. 2. The method of claim 1, wherein determining the value of the nonlinearity comprises determining the value of the nonlinearity based on a comparison of noise gating of the magnitude of the drive signal to noise gating of the magnitude of the sense signal.

6. determining the value of the nonlinearity, generating said drive signal, which is a pilot tone, at a frequency higher than a resonant frequency of an electromechanical transducer; measuring a total harmonic distortion present in the sense signal in response to the pilot tone; determining a value of the nonlinearity based on the total harmonic distortion; The method of claim 1 , comprising:

7. determining the value of the nonlinearity based on the sensed signal includes measuring a harmonic content of the sensed signal; and the method further comprising determining an orientation of the electromagnetic transducer based on an amplitude and a phase of a harmonic content of the sensed signal. The method of claim 1.

8. The method of claim 1 , further comprising attenuating the drive signal based on the gain.

9. the drive signal is a voltage signal; and the sensed signal is a current signal; 9. The method according to any one of claims 1 to 8.

10. The method of claim 1 , wherein the electromagnetic transducer is one of a tactile transducer, a voice coil, and a loudspeaker.

11. 1. A system for determining and reducing excess 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 applied to the electromechanical transducer; determining a value of nonlinearity based on the sensed 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. A nonlinear bias detector configured as follows: A system comprising:

12. The system of claim 11 , wherein determining the value of the nonlinearity based on the sensed signal comprises determining a back electromotive force associated with the electromechanical transducer based on the sensed signal.

13. Determining the value of the nonlinearity determining a first component ratio equal to a ratio of a first frequency band component present in the drive signal to a second frequency band component present in the drive signal; determining a second component ratio equal to a ratio of components in the first frequency band present in the sensed signal to components in the second frequency band; determining a value of the nonlinearity based on a comparison of the first component ratio and the second component ratio; The system of claim 11 , comprising:

14. Determining the value of the nonlinearity determining a first component ratio equal to a ratio of high frequency components present in the drive signal above a particular frequency to low frequency components present in the drive signal below the particular frequency; determining a second component ratio equal to a ratio of high frequency components present in the sensing signal above the particular frequency to low frequency components present in the sensing signal below the particular frequency; determining a value of the nonlinearity based on a comparison of the first component ratio and the second component ratio; The system of claim 11 , comprising:

15. 12. The system of claim 11, wherein determining the value of the nonlinearity comprises determining the value of the nonlinearity based on a comparison of noise gating of a magnitude of the drive signal to noise gating of a magnitude of the sense signal.

16. Determining the value of the nonlinearity generating said drive signal, said pilot tone, at a frequency higher than a resonant frequency of an electromechanical transducer; measuring a total harmonic distortion present in the sensed signal in response to the pilot tone; determining a value of the nonlinearity based on the total harmonic distortion; The system of claim 11 , comprising:

17. determining the value of the nonlinearity based on the sensed signal includes measuring a harmonic content of the sensed signal; and and determining an orientation of the electromagnetic transducer based on an amplitude and a phase of a harmonic content of the sensed signal. The system of claim 11.

18. 18. The system of claim 11, wherein the non-linear bias detector is further configured to attenuate the drive signal based on the gain.

19. the drive signal is a voltage signal; and the sensed signal is a current signal; A system according to any one of claims 11 to 18.

20. 20. The system of claim 11, wherein the electromagnetic transducer is one of a tactile transducer, a voice coil, and a loudspeaker.

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