Detection and Prevention of Nonlinear Offsets in Haptic Actuators

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

Technical Field

[0001] The present disclosure generally relates to methods, apparatus, and 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

[0002] Vibrotactile transducers, such as linear resonant actuators (LRAs), are widely used in portable devices such as mobile phones to generate vibration feedback to the user. 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.

[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 certain desired vibration patterns. For example, a sharp, distinct vibration pattern on a user's finger can be used to create the sensation of a mechanical button click. This distinct vibration can then be used as a virtual switch to replace a mechanical button.

[0004] FIG1 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 vibrotactile 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, for example, include a pressure or force sensor on a screen or virtual button of the device 100.

[0005] Among various forms of vibro-tactile feedback, sustained tonal vibrations can play an important role in notifying the user of a device of certain predetermined events, such as incoming calls or messages, emergency alerts, and timer warnings. To effectively generate tonal vibration notifications, it may be desirable to operate the tactile actuator at or near its resonant frequency.

[0006] The resonant frequency f0 of the tactile transducer can be approximately estimated as:

[0007]

[0008] 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.

[0009] 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 varying strengths with which a user grips the device.

[0010] Figure 2 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 driver amplifier output voltage waveform V(t) is shown, where the output impedance Ro is. The terminal voltage V T (t) can be sensed across the terminals of the tactile transducer.The mass-spring system 201 moves with velocity u(t).

[0011] Haptic systems may require precise control over the motion of the tactile transducer. This control can rely on the magnetic coefficient Bl, also known as the electromagnetic transfer function of the tactile transducer. Ideally, 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 conductor within the magnetic field that produces the magnetic flux density B. In the ideal case of motion along a single axis, the magnetic flux density B and the length l should remain constant.

[0012] As mentioned above, when electric current passes through the coil of electromagnet, due to the interaction of electromagnet and permanent magnet, electromagnet can be subjected to force.Oscillating actuator 103 can be mechanically mounted on the structure of equipment 100 so that the vibration caused by moving mass is transferred to the equipment, thereby can be felt by the user.In most portable electronic devices, oscillating actuator 103 is driven with voltage waveform by low output impedance amplifier 102. However, due to the acceleration of mass in oscillating actuator 103, the user may experience tactile event, and this mass interacts with the rest of equipment 100 and the hand of the user.

[0013] For a given steady-state input voltage signal, the LRA's response may become increasingly nonlinear as the voltage amplitude increases beyond a certain limit (typically specified by the LRA manufacturer as a maximum voltage level). This nonlinearity is typically caused by amplitude-dependent variations in the spring constant associated with the springs suspending the LRA's internal mass. This amplitude dependence is typically most pronounced at higher voltage levels. Depending on the LRA's structure, a sufficiently large input signal driven at or near the resonant frequency may displace the LRA's internal mass to the point of contact with the LRA's housing or its mechanical end stops. This behavior is often referred to as overexcursion. This condition can negatively impact the user experience and, in some cases, can even cause physical damage to the LRA. Therefore, systems and methods for detecting and preventing this overexcursion may be desirable. Summary of the Invention

[0014] 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.

[0015] According to an embodiment of the present disclosure, a method for determining and mitigating excessive 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 excessive excursion of the internal mass, and applying a gain to a signal path configured to generate the drive signal based on the probability.

[0016] According to these and other embodiments of the present disclosure, a system for determining and mitigating excessive 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 excursion detector configured to determine a nonlinearity value based on the sensed signal, map the nonlinearity value to a probability of excessive excursion of the internal mass, and apply a gain to a signal path configured to generate the drive signal based on the probability.

[0017] 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.

[0018] 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 disclosure, as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] A more complete understanding of the present embodiment and its 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:

[0020] FIG1 shows an example of a vibrotactile system in a device known in the art;

[0021] FIG2 shows an example of a linear resonant actuator (LRA) modeled as a linear system as known in the art;

[0022] Figure 3 shows selected components of an example host device according to an embodiment of the present disclosure;

[0023] Figure 4 shows a cross-sectional view of an example electromagnetic load implemented as a tactile transducer according to an embodiment of the present disclosure; and

[0024] Figure 5 Graph illustrating example gains that a waveform pre-processor may apply to a raw transducer drive signal as a function of over-excursion probability to generate a processed transducer drive signal in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION

[0025] 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 employed in place of or in conjunction with the embodiments discussed below, and all such equivalent techniques are intended to be encompassed by this disclosure.

[0026] 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 mechanical vibration). For example, many electronic devices may include one or more speakers or microphones for sound generation, such as for playback of audio content, voice communication, and / or for providing audible notifications.

[0027] 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 communication.

[0028] 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 the 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 aforementioned accessory device when connected. Such electronic devices will therefore include drive circuitry for driving the transducers 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, e.g., a time-varying waveform.

[0029] Figure 31 shows selected components of an example host device 300 that incorporates force sensing using an electromagnetic load 301 in the host device 300, according to an embodiment of the present disclosure. 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 microspeaker, a piezoelectric transducer, or other suitable transducer.

[0030] Briefly go to Figure 4 , Figure 4 FIG. 3 shows a cross-sectional view of an example electromagnetic load 301 implemented as a tactile transducer according to an embodiment of the present disclosure. Figure 4 As shown, 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., Figure 4 4. The housing 404 may include end stops 410 configured to engage corresponding features 412 of the moving mass 402 to limit the deflection of the moving mass 402 within the housing 404. As described above, the mechanical contact between the features 412 and the end stops 410 may result in a nonlinearity between the electromagnetic signal driving the electromagnetic load 301 and the displacement or deflection of the moving mass 402 relative to the housing 404.

[0031] Go to again Figure 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) (in some embodiments, the signal may be a waveform signal, such as a tactile waveform signal or an audio signal). The raw transducer drive signal x′(t) may be generated based on a desired playback waveform received by the signal generator 324.

[0032] The raw transducer drive signal x′(t) may be received by a waveform pre-processor 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.

[0033] The processed transducer driving signal x(t) can be further amplified by the amplifier 306 to generate a driving signal V(t) for driving the electromagnetic load 301. In response to the driving signal V(t), the sensing terminal voltage V T(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) can be sensed across a shunt resistor 302 having a resistance R coupled to the terminals of the electromagnetic load 301. s .

[0034] like Figure 3 As shown, the processing subsystem 305 may include a nonlinear offset detector 308 configured to detect a nonlinear offset based on the sensed terminal voltage V T (t) and the sensed current I(t), determine whether there is nonlinearity between the electromagnetic signal driving the electromagnetic load 301 and the displacement of the moving mass block (e.g., the moving mass block 402) of the electromagnetic load 301, and determine the probability P of excessive offset of the moving mass block based on this nonlinearity.

[0035] To illustrate the function of the nonlinear offset detector 308, the nonlinear offset detector 308 can estimate the back EMF voltage V of the electromagnetic load 301. B (t). Generally speaking, the back EMF voltage V B (t) may not be directly measurable from outside the tactile transducer. However, the terminal voltage V T (t) can be compared with V B (t) has the following relationship:

[0036]

[0037] where the parameters are defined as described in reference Figure 2. Therefore, the back EMF voltage V B (t) can be estimated according to equation (2), which can be rearranged as:

[0038]

[0039] Because the back EMF voltage V B (t) is proportional to the velocity of the moving mass of the electromagnetic load 301, so the back EMF voltage V B (t) can then provide an estimate of this speed. Therefore, the back EMF voltage V can be estimated based on the equivalent electrical model of the electromagnetic load 301. B (t), and this electrical model may vary according to the parameters of the electromagnetic load 301 and the host device 300 (including the resonant frequency and the quality factor).

[0040] 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 specifications may be sufficient. For example, in some embodiments, the nonlinear offset detector 308 can determine the estimated back EMF voltage V according to the teachings of U.S. patent application Ser. No. 16 / 559,238, filed Sep. 3, 2019, the entire contents of which are incorporated herein by reference. B (t).

[0041] By measuring the sense current I(t) and the back EMF voltage V B (t), the nonlinear offset detector 308 can estimate the internal state of the electromagnetic load 301. B Based on the amount of nonlinearity observed relative to a threshold, the nonlinear excursion detector 308 can control the processed transducer drive signal x(t) to prevent excessive excursion.

[0042] Reference again Figure 4 If spring 406 of electromagnetic load 301 is overstretched, moving mass 402 may exhibit nonlinear behavior with respect to the processed sensor drive signal x(t). Furthermore, collisions between moving mass 402 and end stop 410 may also cause nonlinear distortion. These two conditions define a nonlinear behavior region where electromagnetic load 301 is more likely to overexert.

[0043] To determine the likelihood or probability of an excessive excursion, the nonlinear excursion detector 308 may use electrical measurements (e.g., the terminal voltage V T (t), sensing current I(t), back EMF voltage V B (t)) to determine the occurrence of nonlinearity.

[0044] For example, when the processed transducer drive signal x(t) is non-periodic, as is the case with the haptic playback waveform during operation of the host device 300, the haptic playback waveform can be determined by comparing it with the terminal voltage V T The voltage content ratio associated with the sense current I(t) and the current-voltage ratio associated with the sense current I(t) are used to determine the probability P of excessive excursion. The voltage content ratio may include the terminal voltage V above a certain frequency. T The high-frequency content in (t) and the terminal voltage V below a specific frequency TThe current content ratio can be the ratio of the low-frequency content present in the sensed current I(t) to the low-frequency content present in the sensed current I(t) above a specific frequency. Similarly, the current content ratio can include the ratio of the high-frequency content present in the sensed current I(t) above a specific frequency to the low-frequency content present in the sensed 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 an overexcursion.

[0045] In addition to or instead of comparing the current content ratio to the voltage content ratio, the nonlinear offset detector 308 may also be based on whether the noise gating of the amplitude of the sense current I(t) is triggered without triggering the terminal voltage V T The probability P of over-excursion is determined by noise gating the amplitude of (t).

[0046] As another example, in an offline process where no haptic waveform is generated, the signal generator 324 can generate a raw transducer drive signal x′(t), a pilot tone higher than the resonant frequency of the electromagnetic load 301, and the nonlinear offset detector 308 can generate a raw transducer drive signal x′(t) based on the sensed current I(t) and the terminal voltage V T The total harmonic distortion (THD) of the pilot tone caused by the electromagnetic load 301 entering a nonlinear behavior region can be measured using the nonlinear excursion detector 308. This THD can be calculated as a function of the pilot tone and its harmonics. The nonlinear excursion detector 308 can also map the measured THD to a probability of excessive excursion at a specific frequency and / or amplitude, which can be used by the waveform pre-processor 326 to generate the processed transducer drive signal x(t).

[0047] 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 to eliminate or reduce the occurrence of the moving mass 402 exceeding a rated excursion limit and / or other operational limits (e.g., manufacturer-defined limits of the electromagnetic load). For example, Figure 5 Graph illustrating example gains 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 to generate the processed transducer drive signal x(t) in accordance with an embodiment of the present disclosure.

[0048] Based on the foregoing, 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 haptic actuator can be provided, wherein a nonlinearity value of the electromagnetic load can be measured based on at least a current signal associated with the electromagnetic load (e.g., sense current I(t)). The nonlinearity value can be mapped to a likelihood value (e.g., probability P) of excessive excursion of the moving mass. Furthermore, the likelihood value can be used to determine a gain reduction applied to a transducer drive signal.

[0049] 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.

[0050] This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that would be understood by a person of ordinary skill in the art. Similarly, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that would be understood by a person of ordinary skill in the art, where appropriate. In addition, in the appended claims, references to a device or system or component of a device or system adapted to, arranged to, capable of, configured to, enabled to, operable to, or operable to perform a particular function encompass that device, system, or component, regardless of whether it or that particular function is activated, turned on, or unlocked, as long as the device, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operable. Therefore, the systems, devices, and methods described herein may be modified, added to, or omitted without departing from the scope of this disclosure. 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 methods described 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.

[0051] 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 embodiments and techniques shown in the drawings and described above.

[0052] Unless specifically noted otherwise, items depicted in the drawings are not necessarily drawn to scale.

[0053] 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 to be 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.

[0054] Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Additionally, other technical advantages may become apparent to one of ordinary skill in the art after reviewing the above drawings and descriptions.

[0055] To assist the Patent Office and any reader of any patent issuing based on 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

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; as well as A gain is applied to a signal path configured to generate the drive signal based on the probability.

2. The method according to claim 1, wherein Determining the nonlinear value based on the sense signal includes determining a back electromotive force associated with the electromechanical transducer based on the sense signal.

3. The method according to claim 1, wherein Determining the nonlinear value includes: 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 according to claim 1, wherein Determining the nonlinear value includes: 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 according to claim 1, wherein Determining the nonlinearity value includes determining the nonlinearity value based on a noise gating of an amplitude of the drive signal compared to a noise gating of an amplitude of the sense signal.

6. The method according to claim 1, wherein Determining the nonlinear value includes: 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 sensed signal in response to the pilot tone; and The nonlinearity value is determined based on the total harmonic distortion. The method of claim 1 , further comprising attenuating the drive signal based on the gain.

8. The method according to claim 1, wherein: Determining the nonlinearity value based on the sensed signal includes measuring a harmonic component of the sensed signal; and The method also includes determining an orientation of the electromagnetic transducer based on the amplitude and phase of the harmonic component of the sense signal.

9. The method according to claim 1, wherein: The driving signal is a voltage signal; and The sensing signal is a current signal.

10. The method according to claim 1, 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 nonlinear offset detector 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; as well as A gain is applied to a signal path configured to generate the drive signal based on the probability.

12. The system according to claim 11, wherein Determining the nonlinear value based on the sense signal includes determining a back electromotive force associated with the electromechanical transducer based on the sense signal.

13. The system according to claim 11, wherein: Determining the nonlinear value includes: 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 according to claim 11, wherein: Determining the nonlinear value includes: 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 according to claim 11, wherein Determining the nonlinearity value includes determining the nonlinearity value based on a noise gating of an amplitude of the drive signal compared to a noise gating of an amplitude of the sense signal.

16. The system according to claim 11, wherein Determining the nonlinear value includes: 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 sensed signal in response to the pilot tone; and The nonlinearity value is determined based on the total harmonic distortion.

17. The system according to claim 11, wherein: The non-linear offset detector is further configured to attenuate the drive signal based on the gain.

18. The system of claim 11, wherein: Determining the nonlinearity value based on the sensed signal includes measuring a harmonic component of the sensed signal; and The system also determines an orientation of the electromagnetic transducer based on the amplitude and phase of the harmonic component of the sensed signal.

19. The system of claim 11, wherein: The driving signal is a voltage signal; and The sensing signal is a current signal.

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

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