CN112925410A

CN112925410A - Method and system for estimating coil impedance of electromagnetic transducer

Info

Publication number: CN112925410A
Application number: CN202011439337.4A
Authority: CN
Inventors: 伊曼纽尔·马查斯; 乔恩·亨德里克斯
Original assignee: Cirrus Logic International Semiconductor Ltd
Current assignee: Cirrus Logic International Semiconductor Ltd
Priority date: 2019-12-05
Filing date: 2020-12-07
Publication date: 2021-06-08
Also published as: GB202212788D0; GB2592462B; GB2608906B; GB2608906A; GB202018051D0; GB2592462A

Abstract

A method may include selecting, based on a state of an electromagnetic load, a selected measurement technique from a plurality of impedance measurement techniques for measuring an impedance of the electromagnetic load, and performing the selected measurement technique to generate an estimate of the impedance of the electromagnetic load.

Description

Method and system for estimating coil impedance of electromagnetic transducer

RELATED APPLICATIONS

The present disclosure claims priority to U.S. provisional patent application serial No. 62/944, 090, filed 2019, 12, 5, which is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates generally to estimating coil impedance of electromagnetic transducers, particularly haptic transducers.

Background

Vibrotactile transducers, such as Linear Resonant Actuators (LRAs), are widely used in portable devices, such as mobile phones, to generate vibratory feedback to a user. Various forms of vibrotactile feedback create different tactile sensations to the user's skin and may play an increasingly important role in the human-computer interaction of modern devices.

The LRA can be modeled as a mass-spring electromechanical vibration system. When driven with a suitably designed or controlled drive signal, the LRA may produce some desired form of vibration. For example, strong and distinct vibration patterns on a user's finger may be used to create a sensation that mimics a mechanical button click. This distinct vibration may then act as a virtual switch instead of a mechanical button.

Fig. 1 shows an example of a vibrotactile system in a device 100. The apparatus 100 may include a controller 101 configured to control a signal applied to an amplifier 102. The amplifier 102 may then drive the haptic transducer 103 based on the signal. The controller 101 may be triggered by a flip-flop to output to the signal. For example, the trigger may include a pressure or force sensor on a screen or virtual button of device 100.

In various forms of vibrotactile feedback, a sustained tonal vibration can play an important role in notifying the user of the device of certain predetermined events, such as an incoming call or text message, an emergency alert, a timer alert, and the like. To efficiently produce tonal vibration notifications, it may be desirable to operate the haptic vibrator at its resonant frequency.

Resonant frequency f of a haptic transducer₀Can be approximated as:

where C is the compliance of the spring system (compliance) 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 the tactile transducer may change from time to time due to temporary component changes caused by inter-sample differences of individual tactile transducers, mobile device assembly differences, aging, and changes in usage conditions, such as various different forces with which a user holds the device.

Fig. 2A shows an example of a Linear Resonant Actuator (LRA) modeled as a linear system including a mass-spring system 201. LRAs are nonlinear components whose behavior may vary due to, for example, applied voltage levels, operating temperatures, and operating frequencies. However, in some states, these components may be modeled as linear components.

Fig. 2B shows an example of an LRA modeled as a linear system, which includes an electrical equivalent model of a mass-spring system 201 of the LRA. In this example, the LRA is modeled as a third order system with electrical and mechanical components. In particular, Re and Le are the direct current resistance and coil inductance, respectively, of the coil-magnet system; and Bl is the magnetic force factor of the coil. The driver amplifier outputs a voltage waveform v (t) with an output impedance Ro. Terminal voltage V_T(t) may be sensed across terminals of the tactile transducer. The mass-spring system 201 moves at a velocity u (t).

By which the impedance Z of an electromagnetic load, such as an LRA, can be_LRACharacterisation, impedance Z_LRACan be regarded as the coil impedance Z_coilAnd a mechanical impedance Z_mechThe sum of (1):

Z_LRA＝Z_coil+Z_mech (2)

coil impedance Z_coilAnd may further include a Direct Current (DC) resistor Re in series with the inductor Le:

Z_coil＝Re+s*Le (3)

mechanical impedance Z_mechCan be defined by three parameters, including a resonant resistance R representing the resistance representing the mechanical friction of the mass-spring system of the tactile transducer_RESCapacitance C representing the capacitance of the equivalent moving mass M of the mass-spring system of the tactile transducer_MESAnd an inductance L representing the compliance C of the mass-spring system of the haptic transducer_CES. The electrical equivalent of the total mechanical impedance is R connected in parallel_RES，C_MES，L_CES. The laplace transform of the parallel connection is described as:

resonant frequency f of a haptic transducer₀Can be expressed as:

the quality factor Q of the LRA can be expressed as:

referring to equation (6), this expression relates to describing the resistances Re and R_RESIs connected in parallel (i.e. a sub-expression of

) Whereas in fig. 2B these resistors are shown in a series connection, this may not appear intuitive. This may be the case, however, in the case where the drive voltage Ve oscillates, but then switches off abruptly and approaches zero. The voltage amplifier shown in fig. 2B can be considered to have a low source impedance, ideally zero source impedance. In this state, when the drive voltage Ve tends to zero, the voltage amplifier efficiently disappears from the circuit. At this time, the top end of the resistor Re and the resistor R in FIG. 2B_RESIs equally grounded, and therefore, resistors Re and R_RESIndeed a parallel connection as shown in equation (6).

Electromagnetic transducers such as LRAs or micro-speakers may have slow response times. Fig. 3 is a graph of an example response of an LRA depicting a drive signal to the LRA, a current through the LRA, and a back electromotive force (back EMF) of the LRA, where the back EMF may be proportional to a velocity of a moving element (e.g., a coil or magnet) of the transducer. As shown in fig. 3, the back EMF start time may slow as energy is delivered to the LRA, and some "ringing" of the back EMF may occur after the end of the drive signal as the mechanical energy stored in the LRA is discharged. In the case of a haptic LRA, such a behavioral characteristic may result in a "soft" haptic click or pulse (pulse), rather than a "crisp" haptic response. Thus, it may be desirable for the LRA to instead have a response similar to that shown in fig. 4, where there is minimal ringing after the end of the drive signal, and a more "crisp" haptic response may be provided in the case of haptics. Thus, it may be desirable to apply processing to the drive signals such that the velocity or back EMF of the transducer is closer to that of fig. 4 when the processed drive signals are applied to the transducer.

Disclosure of Invention

In accordance with the teachings of the present disclosure, disadvantages and problems associated with estimating a coil resistance of an electromagnetic transducer may be reduced or eliminated.

In accordance with an embodiment of the present disclosure, a method may include selecting, based on a state of an electromagnetic load, a selected measurement technique from a plurality of impedance measurement techniques for measuring an impedance of the electromagnetic load, and executing the selected measurement technique to generate an estimate of the impedance of the electromagnetic load.

In accordance with these and other embodiments of the present disclosure, a system for estimating an impedance of an electromagnetic load may be configured to select, based on a state of the electromagnetic load, a selected measurement technique for measuring the impedance of the electromagnetic load from a plurality of impedance measurement techniques, and execute the selected measurement technique to generate an estimate of the impedance of the electromagnetic load.

In accordance with some and other embodiments of the present disclosure, a master device may include an electromagnetic load, and a subsystem coupled to the electromagnetic load and configured to select, based on a state of the electromagnetic load, a selected measurement technique for measuring an impedance of the electromagnetic load from a plurality of impedance measurement techniques, and execute the selected measurement technique to generate an estimate of the impedance of the electromagnetic load.

The technical advantages of the present disclosure, as embodied in the drawings, the description and the claims, will be readily apparent to those having ordinary skill in the art. The objects and advantages of the embodiments will be realized and attained by at least 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 only and are not restrictive of the claims as claimed.

Drawings

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

FIG. 1 shows an example of a vibrotactile system in a device known in the art;

FIGS. 2A and 2B respectively illustrate examples of Linear Resonant Actuators (LRAs) modeled as linear systems known in the art;

FIG. 3 illustrates a graph of an example waveform of an electromagnetic load known in the art;

FIG. 4 illustrates a diagram of a desired example waveform of an electromagnetic load according to an embodiment of the present disclosure;

FIG. 5 illustrates a block diagram of selected components of an example mobile device, in accordance with an embodiment of the present disclosure;

FIG. 6 shows a block diagram of selected components of an example integrated haptics system according to an embodiment of the present disclosure;

FIG. 7 illustrates an example system for improving transducer dynamics in accordance with an embodiment of the present disclosure;

FIG. 8 shows an example of a Linear Resonant Actuator (LRA) modeled as a linear system and including a negative resistance, in accordance with an embodiment of the present disclosure;

FIG. 9 shows a flowchart of example operations of a haptic state machine according to an embodiment of the present disclosure;

FIG. 10 shows a flowchart of example operations of a haptic state machine when using a thermal model for coil impedance estimation, according to an embodiment of the present disclosure;

FIG. 11 shows a flowchart of example operations of a haptic state machine when coil impedance estimation is performed using background calibration (background calibration), according to an embodiment of the present disclosure; and

fig. 12A and 12B (which may be collectively referred to herein as fig. 12) show tables summarizing possible voice coil impedance estimation methods that may be employed by a haptic state machine according to the present disclosure.

Detailed Description

The following description sets forth exemplary embodiments in accordance with the present disclosure. Further exemplary embodiments and implementations will be apparent to those of ordinary skill in the art. Further, those of ordinary skill in the art will recognize that a variety of equivalent techniques may be used in place of or in combination with the embodiments discussed below, and all such equivalents are intended to be encompassed by the present disclosure.

Various electronic or smart devices may have a transducer, a speaker, and an acoustic output transducer, e.g., any transducer for transforming a suitable electrical drive signal into an acoustic output, such as an acoustic pressure wave or mechanical vibration. For example, a plurality of electronic devices may include one or more speakers or microphones for producing sound, e.g., for playing back audio content, voice communication, and/or for providing sound notifications.

Such a speaker or microphone may include an electromagnetic actuator, such as a voice coil motor, mechanically coupled to a flexible diaphragm (e.g., a conventional speaker cone) or to a surface of a device (e.g., a glass screen of a mobile device). Some electronic devices may also include an acoustic output transducer capable of generating ultrasonic waves, for example for close-range detection type applications and/or machine-to-machine communication.

The plurality of electronic devices may additionally or alternatively include a more specialized acoustic output transducer (e.g., a haptic transducer) that is customized to produce vibrations for the user for haptic control feedback or notifications. Additionally or alternatively, the electronic device may have a connector (e.g. a socket) for forming a detachable mating connection with a corresponding connector of the accessory device, and may be arranged to provide a drive signal to the connector to drive one or more types of transducers of the accessory device mentioned above when connected. Thus, the electronic device will include a drive circuit for driving the transducer of the host device or the connected accessory with a suitable drive signal. For acoustic or tactile transducers, the drive signal is typically an analog time-varying voltage signal, such as a time-varying waveform.

FIG. 5 illustrates a block diagram of selected components of an example master device 502, according to an embodiment of the disclosure. As shown in fig. 5, master device 502 may include a housing 501, a controller 503, a memory 504, a force sensor 505, a microphone 506, a linear resonant actuator 507, a radio transmitter/receiver 508, a speaker 510, and an integrated haptic system 512.

Housing 501 may include any suitable housing, chassis, or other enclosure for housing the various components of master device 502. The housing 501 may be constructed of plastic, metal, and/or any other suitable material. Further, the housing 501 may be adapted (e.g., sized and shaped) such that the host device 502 may be easily carried on the body of a user of the host device 502. Thus, the host device 502 may include, but is not limited to, a smart phone, a tablet device, a handheld computing device, a personal digital assistant, a laptop computer, a video game controller, or other device that may be easily carried on the body of a user of the host device 502.

Controller 503 may be housed within housing 501 and may include any system, device, or apparatus configured to interpret and/or execute program instructions and/or process data and may include, but is not limited to, a microprocessor, microcontroller, Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC), or any other digital or analog circuitry configured to interpret and/or execute program instructions and/or process data. In some embodiments, the controller 503 interprets and/or executes program instructions and/or process data stored in the memory 504 and/or other computer-readable media that are accessible to the controller 503.

Memory 504 may be housed within housing 501, may be communicatively coupled with controller 503, and may include any system, device, or apparatus (e.g., a computer-readable medium) configured to hold program instructions and/or data for a period of time. Memory 504 may include Random Access Memory (RAM), Electrically Erasable Programmable Read Only Memory (EEPROM), a Personal Computer Memory Card International Association (PCMCIA) card, flash memory, magnetic memory, magneto-optical memory, or any suitable selection and/or array of volatile or non-volatile memory that retains data after host device 502 is powered down.

A microphone 506 may be housed at least partially within the housing 501, which may be communicatively coupled with the controller 503, and may include any system, device, or apparatus configured to transform sound incident at the microphone 506 into electrical signals that may be processed by the controller 503, where such sound is transformed into electrical signals using a diaphragm or membrane having a capacitance that changes based on acoustic vibrations received at the diaphragm or membrane. The microphone 506 may include an electrostatic microphone, a capacitive microphone, an electret microphone, a microelectromechanical system (MEMS) microphone, or any other suitable capacitive microphone.

A radio transmitter/receiver 508 may be housed within the housing 501, which may be communicatively coupled with the controller 503, and may comprise any system, device, or apparatus configured to generate and transmit radio frequency signals with the aid of an antenna and to receive radio frequency signals and to transform information carried by the received signals into a form usable by the controller 503. The radio transmitter/receiver 508 may be configured to transmit and/or receive various types of radio frequency signals, including, but not limited to, cellular communications (e.g., 2G, 3G, 4G, LTE, etc.), short-range wireless communications (e.g., bluetooth), commercial radio signals, television signals, satellite radio signals (e.g., GPS), wireless fidelity, etc.

A speaker 510, which may be housed at least partially within or external to the housing 501, may be communicatively coupled to the controller 503, and may include any system, device, or apparatus configured to generate sound in response to an electrical audio signal input. In some embodiments, the speaker may comprise a dynamic speaker employing a lightweight diaphragm mechanically coupled to a rigid frame by a flexible suspension that constrains the voice coil from moving axially through a cylindrical magnetic gap. When an electrical signal is applied to the voice coil, a magnetic field is generated by the current in the voice coil, making it a variable electromagnet. The magnetic systems of the coil and driver interact to produce a mechanical force that moves the coil (and attached cone) back and forth, reproducing sound under the control of an applied electrical signal from an amplifier.

Force sensor 505 may be housed within 501 housing and may comprise any suitable system, apparatus, or device for sensing a force, pressure, or touch (e.g., interaction with a human finger) and generating an electrical or electronic signal in response to such force, pressure, or touch. In some embodiments, the electrical or electronic signal may be a function of the magnitude of the force, pressure, or touch applied to the force sensor. In these and other embodiments, such electronic or electrical signals may include general purpose input/Output Signals (GPIOs) associated with input signals given by haptic feedback. Force sensor 505 may include, but is not limited to, a capacitive displacement transducer, an inductive force sensor (e.g., a resistive-inductive-capacitive sensor), a strain gauge, a piezoelectric force sensor, a force sensing resistor, a piezoelectric force sensor, a thin film force sensor, or a quantum tunneling composite based force sensor. For clarity in this disclosure, the term "force" is used herein to refer not only to force, but also to physical quantities indicative or analogous to force, such as, but not limited to, pressure and touch.

Linear resonant actuator 507 may be housed within housing 501 and may comprise any suitable system, device, or apparatus for generating an oscillating mechanical force across a single axis. For example, in some embodiments, linear resonant actuator 507 may rely on an alternating voltage to drive a voice coil that presses against a moving mass connected to a spring. When the voice coil is driven at the resonant frequency of the spring, the linear resonant actuator 507 may vibrate with an appreciable force. Thus, the linear resonant actuator 507 may be useful in haptic applications in a particular frequency range. Although the present disclosure is described with respect to using linear resonant actuator 507 for purposes of clarity and illustration, it will be understood that any other type of vibratory actuator (e.g., an eccentric rotating mass actuator) may be used in place of or in addition to linear resonant actuator 507. Further, it is understood that an actuator arranged to generate an oscillating mechanical force across multiple axes may be used instead of or in addition to linear resonant actuator 507. As described elsewhere in this disclosure, the linear resonant actuator 507 may provide haptic feedback to a user of the master device 502 based on signals received from the integrated haptic system 512 for at least one of replacement of mechanical buttons and capacitive transducer feedback.

Housed within 501, is an integrated haptic system 512, which may be communicatively coupled with the force sensor 505 and the linear resonant actuator 507, and may comprise any system, device, or apparatus configured to receive a signal from the force sensor 505 indicative of a force applied to the host device 502 (e.g., a force exerted by a human finger on a virtual button of the host device 502), and to generate an electronic signal for driving the linear resonant actuator 507 in response to the force exerted on the host device 502. Fig. 6 depicts details of an example of an integrated haptic system according to an embodiment of the present disclosure.

Although certain example components (e.g., controller 503, memory 504, force sensor 506, microphone 506, radio transmitter/receiver 508, speaker 510) are depicted above in fig. 5 as being integrated on the master device 502, the master device 502 may include one or more components not specifically enumerated above in accordance with the present disclosure. For example, although FIG. 5 depicts certain user interface components, the master device 502 may include one or more other user interface components (including but not limited to a keyboard, a touch screen, and a display) in addition to the user interface components depicted in FIG. 5, allowing a user to interact with the master device 502 and/or otherwise manipulate the master device 502 and its associated components.

FIG. 6 shows a block diagram of selected components of an integrated haptic system 512A, in accordance with an embodiment of the present disclosure. In some embodiments, integrated haptic system 512A may be used to implement integrated haptic system 512 of fig. 5. As shown in FIG. 6, the integrated haptic system 512A may include a Digital Signal Processor (DSP)602, a memory 604, and an amplifier 606.

DSP 602 may include any system, device, or apparatus configured to interpret and/or execute program instructions and/or process data. In some embodiments, the DSP 602 may interpret and/or execute program instructions and/or process data stored in the memory 604 and/or other computer-readable media accessible to the DSP 602.

The memory 604 may be communicatively coupled with the DSP 602 and may include any system, device, or apparatus (e.g., a computer-readable medium) configured to store program instructions and/or data for a period of time. Memory 604 may include Random Access Memory (RAM), Electrically Erasable Programmable Read Only Memory (EEPROM), a Personal Computer Memory Card International Association (PCMCIA) card, flash memory, magnetic memory, magneto-optical memory, or any suitable selection and/or array of volatile or non-volatile memory that retains data after host device 502 is powered down.

The amplifier 606 may be electrically coupled to the DSP 602 and may include circuitry configured to increase the input signal V_IN(e.g., time-varying voltage or current) to produce an output signal V_OUTAny suitable electronic system, device or apparatus. For example, amplifier 606 may use the power of a power supply (not explicitly shown) to increase the amplitude of the signal. Amplifier 606 may include any suitable class of amplifier, including but not limited to a class D amplifier.

In operation, memory 604 may store one or more haptic playback waveforms. In some embodiments, each of the one or more haptic playback waveforms may define a haptic response a (t) as a desired acceleration of a linear resonant actuator (e.g., linear resonant actuator 507) as a function of time. The DSP 602 may be configured to receive a force signal V indicative of a force applied to the force sensor 505_SENSE. The DSP 602 may respond to receiving a force signal V indicative of a sensed force_SENSEOr independently of such receipt, retrieve the haptic playback waveform from memory 604 and process such haptic playback waveform to determine a processed haptic playback signal V_IN. In embodiments where amplifier 606 is a class D amplifier, the processed haptic playback signal V_INMay comprise a pulse width modulated signal. The DSP 602 may respond to receiving a force signal V indicative of a sensed force_SENSECausing a processed haptic playback signal V_INOutput to amplifier 606, and amplifier 606 may be coupled theretoTactile playback signal V of_INAmplifies to generate a haptic output signal V for driving the linear resonant actuator 507_OUT。

In some embodiments, integrated haptic system 512A may be formed on a single integrated circuit, thereby achieving lower latency compared to existing haptic feedback control methods. By having the integrated haptic system 512A as part of a single monolithic integrated circuit, delays between the various interface and system components of the integrated haptic system 512A may be reduced or eliminated.

The problem shown in fig. 3 may be due to the fact that the linear resonant actuator 507 having a higher quality factor q has a resonant frequency f of the linear resonant actuator 507₀With impedance spikes.

Fig. 7 illustrates an example system 700 for improving the dynamic characteristics of an electromagnetic load 701 in accordance with an embodiment of the present disclosure. In some embodiments, system 700 may be integrated into a host device (e.g., host device 502) that contains system 700 and electromagnetic load 701.

In operation, the haptic waveform generator 722 of the system 700 of the master device may generate (in the absence of a pilot tone generated by the pilot tone generator 718) an original transducer drive signal x' (t) that includes a haptic waveform signal or an audio signal. In some embodiments, the raw transducer drive signal x' (t) may be generated based on a haptic waveform stored by the haptic waveform generator 722 or a memory accessible to the haptic waveform generator 722 (e.g., memory 604) and/or a dynamically generated haptic waveform.

The raw transducer drive signal x '(t) may be received by a combiner 726, which may combine the raw transducer drive signal x' (t) with a correction term from a multiplier 725 to produce a transducer drive signal x (t) to effectively cancel some or all of the coil impedance of the electromagnetic load 701, as described in more detail below. As also described below, by effectively reducing the coil resistance of the electromagnetic load 701, the system 700 may also reduce the effective quality factor q of the electromagnetic load 701, which may in turn reduce start-up time and minimize ringing that occurs after the original transducer drive signal has ended. Although fig. 7 depicts a virtual negative resistance applied by the combiner 726, in some embodiments, a negative impedance filter may be applied to the raw transducer drive signal x' (t) to generate the transducer drive signal x (t) to achieve the same or similar effect of effectively reducing the coil impedance of the electromagnetic load 701. An example of such a negative impedance filter is described in U.S. patent application serial No. 16/168,790 entitled "Methods and Systems for Improved Transducer Dynamics," filed on 12/3 2012, which is incorporated herein by reference in its entirety.

The transducer drive signal x (t) may in turn be amplified by an amplifier 706 to produce a drive signal v (t) for driving the electromagnetic load 701. In response to the driving signal V (t), a sense terminal voltage V of the electromagnetic load 701_T(t) may be converted to a digital representation by a first analog-to-digital converter (ADC) 703. Likewise, the sense current i (t) may be converted to a digital representation by the second ADC 704. The current I (t) may have a resistance R across_sIs sensed by shunt resistor 702, which is coupled to a terminal of electromagnetic load 701. Terminal voltage V_T(t) may be sensed by terminal voltage sensing block 707 (e.g., a voltmeter).

As shown in fig. 7, the system 700 may include an impedance estimator 714. Impedance estimator 714 may include any suitable system, device, or apparatus configured to determine a voltage across electromagnetic load 701 based on a sensed terminal voltage V_T(t), sense current i (t), and/or any other measured parameter, estimate one or more components of electrical and/or mechanical impedance of electromagnetic load 701, and generate one or more control signals. For example, one control signal generated by the impedance estimator 714 may include a negative impedance Re _ neg generated based on an estimate of the dc coil impedance Re of the electromagnetic load 701. As another example, the impedance estimator 714 may also generate a voltage offset V_OFFSETAnd a current offset I_OFFSETWhich may be sensed from the terminal voltage V by

combiners

710 and 712, respectively_T(t) and the sense current i (t), respectively, to cancel any measurement offset that may be present and detected by the impedance estimator 714. As yet another example, and as described in more detail belowThe impedance estimator 714 may generate one or more control signals for communicating with the haptic state machine 716.

Also shown in fig. 7 are two Band Pass Filters (BPFs) 730 and 732, one for each offset-cancelled version of the sense terminal voltage V_T(t) and the sense current I (t) are filtered. The band pass filters 730 and 732 may filter out the haptic playback content of the drive signal v (t) from entering the impedance estimator 714 and thus may bias it away from an accurate estimate of the dc coil impedance Re. In some cases (e.g., in the absence of haptic playback), it may be desirable to bypass the use of these band pass filters 730 and 732. As described below with reference to the initial state 904 in fig. 9, such a moment may occur when the initialization Re estimation at low latency must be completed before playback of the haptic waveform. Because the band pass filters 730 and 732 may add delay to the input signal for the impedance estimator 714, it may be desirable to bypass the band pass filters 730 and 732.

Examples of methods for estimating one or more components of the electrical and/or mechanical impedance of the electromagnetic load 701 and generating a negative coil impedance value Re _ neg are described in (but not limited to): U.S. patent application Ser. No. 16/816,790 entitled "Methods and Systems for Improving Transducer Dynamics" filed 3, 12/2020; U.S. patent application Ser. No. 16/816,833 entitled "Methods and Systems for Estimating Transducer Parameters," filed 3, 12/2020; U.S. patent application Ser. No. 16/842,482 entitled "Thermal Model for Thermal Protection and Resistance Estimation" filed on 7.4.2020; and us patent application serial No. 16/369,556 entitled "Driver circuit" filed on 29/3/2019, all of which are incorporated herein by reference in their entirety.

As mentioned above and described in more detail below, the system 700 may effectively reduce the coil impedance of the electromagnetic load 701 by applying a negative resistance correction term to the original transducer drive signal x' (t) to produce the transducer drive signal x (t), which may reduce the effective quality factor q of the transducer, which may in turn reduce the start-up time and minimize ringing that occurs after the original transducer drive signal has ended. The quality factor q of the transducer can be expressed as:

in equation (7), the molecular term R increases with the direct current resistance Re_RESRe ratio denominator term R_RES+ Re increases more rapidly. Therefore, the quality factor q generally increases with increasing dc resistance Re. Thus, one way in which the system 700 can minimize the quality factor q is to effectively reduce the dc resistance Re. In some embodiments, the system 700 may desirably reduce the effective dc resistance Re to the point where critical damping occurs in the electromagnetic load 701.

Turning briefly to fig. 8, fig. 8 illustrates an example of an electromagnetic load 701 modeled as a linear system that includes an electrical model of an electrical component 802 and a mechanical component 804, and includes a negative resistance resistor 806 having a negative resistance Re _ neg inserted in series with the electromagnetic load 701, in accordance with an embodiment of the present disclosure. The addition of the negative resistance Re can reduce the quality factor q because it effectively subtracts from the dc resistance Re, thereby reducing the overall dc resistance.

In practice, the negative resistor is not present. Conversely, the system 700 may be configured generally like the circuit shown in FIG. 8, including a mathematical model of the negative impedance Re _ neg in series with a mathematical model of the electromagnetic load 701. In operation, as shown in FIG. 8, the system 700 (e.g., at the output of the combiner 726) may actually calculate the voltage V that appears at the junction (junction) of the negative resistance Re _ neg and the direct current resistance Re_mIf, in fact, a physical resistor with a negative resistance Re _ neg can be arranged in series with the electromagnetic load 701. The calculated voltage V can then be used_mTo drive electromagnetic load 701.

In essence, system 700 may implement a sensorless speed control feedback loop for electromagnetic load 701. The feedback loop may use a dynamic estimate of the electromagnetic load 701 parameters and generate feedback (e.g., negative impedance Re _ neg) to cancel most of the electrical and mechanical impedance of the electromagnetic load 701. In the case of the dc coil resistance Re, its estimation must be very accurate (e.g., < 1% error) in order for the feedback loop of the system 700 to achieve stability and achieve the desired negative impedance effect. The electrical and mechanical impedance of the electromagnetic load 701 may change in response to a stimulus applied thereto (e.g., the amplitude and frequency of the drive signal v (t)), an ambient temperature state, and/or other factors.

Returning to fig. 7, system 700 can also include a pilot tone generator 718. Pilot tone generator 718 may comprise any system, device, or apparatus configured to generate a pilot tone substantially below or above the resonant frequency of electromagnetic load 701 in response to one or more control signals received from haptic state machine 716. Thus, pilot tone generator 718 may be capable of driving a signal at a frequency and amplitude that may affect an electrical parameter of electromagnetic load 701 while producing little or no perceptible haptic effect at electromagnetic load 701. As shown in fig. 7, the output of the pilot tone generator 718 may be combined with the output of the haptic waveform generator 722 by a combiner 724.

Haptic state machine 716 may comprise any system, device, or apparatus configured to generate control signals to other components of system 700 to control the operation of such other components in response to haptic trigger events, control signals, and/or other information received from other components of system 700 to sequence the pilot tone generation by pilot tone generator 718, the haptic waveforms generated by haptic waveform generator 722, and the operation of an impedance estimator to accurately and efficiently estimate the coil resistance of electromagnetic load 701 (from a time delay perspective).

To better understand the functionality of haptic state machine 716, various possible states of system 700 and electromagnetic load 701 may illustratively be considered. For example, possible states of electromagnetic load 701 may include:

although the haptic trigger has been received by the system 700, the electromagnetic load 701 has not yet been stimulated to produce a haptic vibration;

a haptic playback event is taking place at electromagnetic load 701 and electromagnetic load 701 is stimulated;

the haptic playback event has just ended and the electromagnetic load 701 is no longer stimulated by the drive signal, but the electromagnetic load 701 may be in motion; or

No haptic playback event occurs for a significant period of time, and the electromagnetic load 701 has not experienced operation since the end of the previous haptic event.

Possible states of the haptic playback waveform generated by the haptic waveform generator 722 may include:

the haptic playback waveform is pre-stored in memory;

the haptic playback waveform is dynamically generated as it is played back;

the haptic playback waveform has spectral content centered around and including a frequency region of the resonant frequency of the electromagnetic load 701;

the haptic playback waveform has significant spectral content in a frequency region below the resonant frequency of the electromagnetic load 701;

the haptic playback waveform has significant spectral content in a frequency region above the resonant frequency of the electromagnetic load 701; and

the haptic playback waveform has significant spectral content in the frequency regions at, below, and above the resonant frequency of the electromagnetic load 701.

Possible states of the pilot tone generated by the pilot tone generator 718 may include:

the pilot tone is at a frequency significantly lower than the resonant frequency of the electromagnetic load 701, so that the impedance of the electromagnetic load is dominated by the dc coil resistance Re;

a low frequency pilot tone can be played during a haptic playback event;

the low frequency pilot tone can be played some minimum amount of time during and after the haptic playback event such that a period of the pilot tone of sufficient period occurs to provide a first estimate of the dc coil resistance Re for frequencies below the resonant frequency of the electromagnetic load 701;

a low frequency pilot tone may be played when a predetermined period of time (e.g., one minute) has elapsed since the end of the previous haptic playback event;

the pilot tone is at a frequency significantly higher than the resonant frequency of the electromagnetic load 701, so that the impedance of the electromagnetic load 701 is dominated by the dc coil resistance Re and the coil inductance Le;

a high frequency pilot tone can be played briefly after the haptic trigger but immediately before playback of the haptic playback waveform (e.g., a sufficiently short period of time such that the user does not perceive a delay between the haptic trigger and the haptic effect in response to the haptic trigger);

a high frequency pilot tone can be played some minimum amount of time during and after the haptic playback event such that a sufficiently periodic pilot tone occurs to provide a first estimate of the dc coil resistance Re for frequencies above the resonant frequency of the electromagnetic load 701; and

the pilot tone is a combination of the above-described low and high frequency tones that are played at some minimum amount of time during and after the haptic playback event, such that a sufficiently periodic tone provides a first estimate of the dc coil resistance Re at frequencies significantly above the resonant frequency of the electromagnetic load 701, the coil resistance Re at frequencies significantly below the resonant frequency of the electromagnetic load 701, and the coil inductance Le.

In all cases, the pilot tone may be at a sufficiently low amplitude such that the user is unable to perceive the presence of the pilot tone through tactile or auditory perception.

To better understand the functionality of the haptic state machine 716, various possible methods for estimating the various entities of the system 700 and the electromagnetic load 704 may also be illustratively considered. For example, possible estimation methods for determining the dc coil resistance Re and the coil inductance Le of the electromagnetic load 701 may include:

a least squares fitting technique to determine the relationship between the voltage and current seen by the electromagnetic load 701;

and

thermal model to predict the change of the dc coil resistance Re over time, which can:

using a timer to track elapsed time between significant events, such as the start of a haptic playback event, the end of a haptic playback event, and the time between haptic events;

for predicting the degree to which electromagnetic load 701 heats up during a haptic playback event;

for predicting the degree to which electromagnetic load 701 cools after a previous haptic playback event; and

for distinguishing changes in the dc coil resistance Re due to heating, cooling, and ambient temperature.

As another example, for determining the voltage offset V_OFFSETAnd a current offset I_OFFSETMay include:

playback of zero value haptic playback signal to estimate sense terminal voltage V_T(t) and a dc offset of the sense current i (t); and

replaying some integer periods of pilot tones in order to estimate the voltage V at the sensing terminal_T(t) and the DC offset of the sense current I (t) (e.g., coil impedances Re and Le can be estimated with the DC offset by a least squares fitting procedure; this approach can provide a low latency approach to obtaining a new estimate of the sensor offset and coil impedance at the time between the haptic trigger and the start of haptic playback;

wherein in either case the sampled values produced by such signals may be separately accumulated and the offset determined by dividing by the number of samples.

As another example, a thermal model may be used to determine the relationship between the voltage and current seen by electromagnetic load 701.

Fig. 9 illustrates a flowchart of example operations of the haptic state machine 716 without coil impedance estimation using a thermal model, according to an embodiment of the disclosure. The haptic state machine 716 may begin in the sleep state 902 after the system 700 is powered on. The tactile state machine 716 can remain in the sleep state 902 until a request for a tactile playback event (e.g., a tactile trigger) is received, at which time the tactile state machine 716 can proceed to the initial state 904.

In the initial state 904, the haptic state machine716 may cause pilot tone generator 718 to play a pilot tone substantially above the resonant frequency of electromagnetic load 701 for an integer period while impedance estimator 714 collects the sense terminal voltage V_T(t) and a sample of the sense current I (t). After the integer period ends, the impedance estimator 714 can estimate a voltage offset V to be applied in the upcoming haptic playback event_OFFSETAnd a current offset I_OFFSETAnd the dc coil resistance Re can also be estimated for frequencies higher than the resonant frequency of the electromagnetic load 701. Once the impedance estimator 714 has completed the voltage offset V_OFFSETCurrent offset I_OFFSETAnd the estimate of the dc coil resistance Re, the haptic state machine 716 may proceed to the playback enabled state 906.

During the playback-enabled state 906, the haptic state machine 716 can cause the haptic waveform generator 722 to play a haptic playback waveform in response to a haptic trigger received during the sleep state 902, and can also cause the pilot tone generator 718 to play a pilot tone substantially below the resonant frequency of the electromagnetic load 701 simultaneously with the haptic playback waveform. In some embodiments, the haptic state machine 716 may cause the pilot tone generator 718 to play a pilot tone substantially above the resonant frequency of the electromagnetic load 701 simultaneously with the haptic playback waveform. Additionally, during the playback enabled state 906, the haptic state machine 716 can cause the impedance estimator 714 to collect the sensed terminal voltage V_T(t) and samples of the sense current I (t), now respectively by the voltage offset V_OFFSETAnd a current offset I_OFFSETTo compensate and the dc coil resistance Re is estimated for frequencies below the resonant frequency of the electromagnetic load 701. In embodiments where the haptic state machine 716 causes the pilot tone generator 718 to play a pilot tone substantially above the resonant frequency of the electromagnetic load 701 simultaneously with the haptic playback waveform during the playback initiation state 906, the impedance estimator 714 may also estimate the dc coil resistance Re and/or estimate the coil inductance Le for frequencies below the resonant frequency of the electromagnetic load 701. If and when a first estimate of the dc coil resistance Re is made for frequencies below the resonant frequency of the electromagnetic load 701, the haptic state machine 716 can proceed to the playback tracking state 908. On the other hand, if and when alreadyRequesting the end of the haptic playback event (e.g., at the end of the haptic playback waveform generated by haptic waveform generator 722 in response to a haptic trigger), haptic state machine 716 can proceed to mute state 910.

As a particular example, the resonant frequency of the electromagnetic load 701 in a haptic application may be 150 Hz. The pilot tone significantly below the resonant frequency may be a tone between 10Hz and 40 Hz. The pilot tone, which is significantly higher than the resonant frequency, may be a tone between 500Hz and 2.5 KHz. Because the human ear may be most sensitive to tones in the 2-KHz range, tones around such frequencies may cause a perceptible acoustic response. To reduce this possibility, a pilot tone significantly above the resonant frequency may be set to a very low signal amplitude (e.g., 100mV) and played back for a very short duration (e.g., 5 milliseconds) between the haptic trigger and the playback of the haptic waveform, such that any residual audio transients are masked by the start (onset) of the haptic playback itself.

In the case where the electromagnetic load 701 does not have an audible response in the region of the pilot tone above the resonant frequency, it may be advantageous to play both the pilot tone below the resonant frequency and the pilot tone above the resonant frequency simultaneously with the transducer drive signal x (t) for a number of reasons. The high frequency pilot may enable an earlier estimation of the dc coil resistance Re in time than the low frequency pilot may be able to provide an estimation of the dc coil resistance Re. In this case, the system 700 can more quickly begin tracking changes in the dc coil resistance Re. As the lower frequency pilot reaches a time to achieve a more accurate estimate of the dc coil resistance Re using the lower frequency pilot rather than the higher frequency pilot, the impedance estimator 714 may switch its output negative impedance Re _ neg accordingly. There may be a tradeoff between the length and accuracy of the estimate-a high frequency pilot may achieve a reasonably accurate estimate faster, but a lower frequency pilot enables a more accurate estimate of the change in the longer term tracking dc coil resistance Re. Because the accuracy of estimating the dc coil resistance Re (e.g., less than 1% error may be required for feedback loop stability, as described above) may be important for the stability and supply value of the feedback control loop, it may be advantageous to play back the two pilot tones together. Finally, the estimation of the lower frequency pilot may be able to provide a calibration reference value for the higher frequency pilot, since the lower frequency pilot may be able to achieve a more accurate estimation. It is known that the dc coil resistance Re may increase with increasing frequency due to eddy current losses in the magnet of the electromagnetic load 701, and therefore the coil impedance estimate with the high frequency pilot tone may be higher than the actual dc coil resistance Re required by the feedback control loop. Having both estimates from the high frequency pilot and the low frequency pilot allows the estimate from the high frequency pilot tone to be calibrated to match the estimate from the low frequency pilot tone in order to infer the unbiased dc coil resistance Re from the estimate based on the high frequency pilot tone. Depending on the construction of the electromagnetic load 701, the difference between the estimates of the low frequency pilot tone and the high frequency pilot tone may be negligible, or may be up to a few percent.

During the replay tracking state 908, the haptic state machine 716 may cause the pilot tone generator 718 to continue playing the one or more pilot tones generated during the replay initiation state 906, may cause the impedance estimator 714 to continue collecting the voltage offsets V respectively_OFFSETAnd a current offset I_OFFSETThe compensated sense terminal voltage and sample of the sense current, and continues to estimate the dc coil resistance Re for frequencies below the resonant frequency of the electromagnetic load 701. In embodiments where the haptic state machine 716 causes the pilot tone generator 718 to play a pilot tone significantly above the resonant frequency of the electromagnetic load 701 concurrently with the haptic playback waveform during the playback initiation state 906 (and the playback tracking state 908), the impedance estimator 714 may also continue to estimate the dc coil resistance Re and/or estimate the coil inductance Le for frequencies below the resonant frequency of the electromagnetic load 701. If and after an end of the haptic playback event has been requested (e.g., at the end of the haptic playback waveform generated by the haptic waveform generator 722 in response to a haptic trigger), the haptic state machine 716 can proceed to the mute state 910.

In mute state 910, haptic state machine 716 may cause haptic waveform generator 722 to stop playing the haptic playback waveform, causing pilot tone generator 718 to ramp down (or step down) the amplitude of any pilot tone or tones it is generating, causing impedance estimator 714 to stop the collection of samples of sense terminal voltage and sense current and the generation of an impedance estimate. This ramp down function may be important because simply stepping down the pilot tone may result in a broadband transient that triggers a human-perceptible acceleration response, and may reduce or eliminate such transient artifacts. During mute state 910, haptic state machine 716 may cause impedance estimator 714 to save all final estimated impedance values and any other estimated values during a haptic playback event (e.g., to a memory accessible to impedance estimator 714). After the pilot tone generator 718 mutes one or more pilot tones, the tactile state machine 716 may again enter the dormant state 902.

Fig. 10 illustrates a flowchart of example operations for a haptic state machine when using a thermal model for impedance estimation, according to an embodiment of the present disclosure.

After system 700 is powered on, haptic state machine 716 can begin in sleep state 1002. Haptic state machine 716 can remain in sleep state 1002 until a request for a haptic playback event (e.g., a haptic trigger) is received, at which time haptic state machine 716 can proceed to initial state 1004. In initial state 1004, haptic state machine 716 may cause haptic waveform generator 722 to playback a zero value waveform for a predetermined time period during which impedance estimator 714 may collect the sense terminal voltage V_T(t) and a sample of the sense current I (t). After the predetermined period of time has ended, the impedance estimator 714 may estimate a voltage offset V to be applied during the upcoming haptic playback event_OFFSETAnd a current offset I_OFFSET. Also during the initial state 1004, the haptic state machine 716 may cause the impedance estimator 714 to use a Thermal Model (e.g., as described in U.S. patent application serial No. 16/842,482 filed on 7/4/2020 and entitled "Thermal Model for Thermal Protection and Resistance Estimation"), a dc coil Resistance Re estimated based on previous haptic playback events, an ambient temperature, and a current coil Resistance Re estimated from previous haptic playback eventsThe initial value of the dc coil resistance Re is estimated from the elapsed time. Once the impedance estimator 714 has completed the voltage offset V_OFFSETCurrent offset I_OFFSETAnd an estimate of the dc coil resistance Re, the haptic state machine 716 may proceed to the playback enabled state 1006.

During the replay initiation state 1006, the haptic state machine 716 may cause the haptic waveform generator 722 to play a haptic replay waveform in response to a haptic trigger received during the sleep state 1002, and may also cause the pilot tone generator 718 to play a pilot tone substantially below the resonant frequency of the electromagnetic load 701 simultaneously with the haptic replay waveform. Additionally, during the playback enabled state 1006, the haptic state machine 716 can cause the impedance estimator 714 to collect the sensed terminal voltage V_T(t) and samples of the sense current I (t), now respectively by the voltage offset V_OFFSETAnd a current offset I_OFFSETTo compensate and the dc coil resistance Re is estimated for frequencies below the resonant frequency of the electromagnetic load 701. Further, in the playback enabled state 1006, the impedance estimator 714 may update its thermal model. If and when the first estimation of the dc coil resistance Re for frequencies below the resonant frequency of the electromagnetic load 701 is completed, the haptic state machine 716 can proceed to the playback tracking state 1008. On the other hand, if and when an end of a haptic playback event has been requested (e.g., at the end of a haptic playback waveform generated by haptic waveform generator 722 in response to a haptic trigger), haptic state machine 716 can proceed to mute state 1010.

During the replay tracking state 1008, the haptic state machine 716 may cause the pilot tone generator 718 to continue to play the pilot tones generated during the replay initiation state 1006, and may cause the impedance estimator 714 to continue to collect the voltage offsets V respectively_OFFSETAnd a current offset I_OFFSETCompensated sense terminal voltage V_T(t) and samples of the sense current i (t), the dc coil resistance Re continues to be estimated for frequencies below the resonant frequency of the electromagnetic load 701, and the thermal model of the impedance estimator 714 continues to be updated. If and when an end of a haptic playback event has been requested (e.g., in response to a haptic trigger, triggered by a haptic sensation)At the end of the haptic playback waveform generated by waveform generator 722), haptic state machine 716 may proceed to mute state 1010.

In mute state 1010, haptic state machine 716 may cause haptic waveform generator 722 to stop playing the haptic playback waveform, cause pilot tone generator 718 to ramp down (or step down) the amplitude of any pilot tones it is generating, and cause impedance estimator 714 to stop sensing terminal voltage V_T(t) and the collection of samples of the sensing current i (t), the generation of an impedance estimate, and the updating of the thermal model. During mute state 1010, haptic state machine 716 may cause impedance estimator 714 to save all final estimated impedance values and any other estimated values during a haptic playback event (e.g., to a memory accessible to impedance estimator 714). Further, during mute state 1010, haptic state machine 716 may cause impedance estimator 714 to reset a timer. After resetting the timer, the haptic state machine 716 may again enter the sleep state 1002. Notably, during the sleep state 1002, when the tactile state machine 716 again enters the initial state 1004, the timer may continue to run so that it can be used (e.g., via a thermal model) to estimate the dc coil resistance.

Fig. 11 illustrates a flowchart of example operations of the haptic state machine 716 when used in the background calibration mode for coil impedance estimation, according to an embodiment of the disclosure. Haptic state machine 716 can begin in sleep state 1102 if a significant amount of time has passed since a previous haptic event. After entering the sleep state 1102, the counter may become active and may reset to some positive predetermined value, e.g., a value corresponding to 60 seconds. A countdown (countdown timer 1103) may then begin, for example, once per second and trend toward zero if no haptic events are requested during this time period. If a haptic event occurs just before the timer expires, the haptic state machine 716 may proceed according to either of FIG. 9 or FIG. 10. However, if no haptic event occurs before the counter expires, the haptic state machine 716 may proceed to the initial state 1104.

In the initial state 1104, the haptic state machine 716 maySuch that the pilot tone generator 718 plays the pilot tone substantially below the resonant frequency of the electromagnetic load 701 for one complete cycle of the pilot tone while the impedance estimator 714 collects the sense terminal voltage V_T(t) and a sample of the sense current I (t). After the pilot tone ends, the impedance estimator 714 can estimate the voltage offset V to be applied the next time it occurs during the next haptic playback event_OFFSETAnd a current offset I_OFFSETAnd also the direct-current coil resistance Re is estimated for frequencies lower than the resonance frequency of the electromagnetic load 701. Once the impedance estimator 714 has completed the voltage offset V_OFFSETCurrent offset I_OFFSETAnd an estimate of the dc coil resistance Re, the haptic state machine 716 may proceed to a mute state 1110.

In the mute state 1110, the haptic state machine 716 may cause the pilot tone generator 718 to ramp down (or step down) the amplitude of the pilot tone it is generating and cause the impedance estimator 714 to cease sensing terminal voltage V_T(t) and collection of samples of the sense current I (t), and generation of an impedance estimate. During the mute state 1110, the haptic state machine 716 may cause the impedance estimator 714 to save all of the final estimated impedance values and any other estimated values during the haptic playback event (e.g., to a memory accessible to the impedance estimator 714). Haptic state machine 716 can again enter sleep state 1102. Notably, during the sleep state 1102, the countdown timer may reset.

Fig. 12 provides a summary of different example methods for estimating coil impedance, all of which may be managed by the haptic state machine 716, shown in various modes in fig. 9, 10 and 11. For example, three different methods for achieving an initial estimate of the dc coil resistance Re prior to playback of the haptic waveform are highlighted in fig. 12. These three methods may form the basis of the mode in which the haptic state machine 716 operates, respectively, where each of fig. 9, 10, and 11 represents one mode. It may be desirable to calculate an initial estimate of the dc coil resistance Re that is as close in time as possible to the request for a haptic event, and without a human perceptible delay between the request for a haptic event and the haptic effect. For example, the haptic event may respond to the pressing of the virtual button with a confirmation (e.g., a brief click or vibration) returned by the device to the user that the virtual button has actually been pressed. The method of achieving an initial estimation of the dc coil resistance Re without appreciable delay is set forth in the first three rows of the table in fig. 12. In two of these three approaches ("thermal model" and "background calibration"), an initial estimate of the dc coil resistance Re may be based on recent past estimates. In one approach ("high frequency pilot estimation"), an initial estimate of the dc coil resistance Re may be formed after the request for the haptic event is completed, but the high frequency pilot approach may estimate Re very quickly (e.g., within 5 milliseconds), such that there is little or no human perceptible delay between the event request and the perceptual effect itself. Achieving a low delay estimate of the dc coil resistance Re may become increasingly important in devices that may employ force sensing virtual buttons, which have their own delay between user interaction with the virtual button and the device hosting the virtual button that actually detects the user interaction. The delay of user interaction detection is typically much longer than the delay of the initial estimate of the dc coil resistance Re using one of the three methods outlined in fig. 12. For this reason, it may be important for a satisfactory user experience that the initial estimate of the dc coil resistance Re is as low as possible, so as not to add a human perceptible delay between the user interacting with the virtual button and receiving a haptic effect confirming the user interaction.

Three different methods for tracking the dc coil resistance Re during playback of the haptic waveform are also highlighted in fig. 12. These three methods are shown in the last three rows of the table of fig. 12. In these approaches, some stimulus (e.g., a high frequency pilot or a low frequency pilot or the haptic waveform itself (if broadband is sufficient)) may be used to stimulate the electromagnetic load 701 so that an estimation technique (such as least squares) may continually estimate the sense terminal voltage V_T(t) and the sensed current i (t) in order to accurately estimate the dc coil impedance Re and possibly the estimated coil inductance Le.

Which of the methods set forth in fig. 12 may be used to achieve an initial estimate of the dc coil impedance Re and a constantly updated estimate of the dc coil impedance Re may depend on the response of the electromagnetic load 701, in particular its acoustic response. During haptic product development, decisions regarding method selection may be made.

While the above discussion applies to linear electromagnetic loads, it should be understood that systems and methods similar or identical to the disclosed systems and methods may be applied to other linear or non-linear systems.

Furthermore, although the above considerations use a negative resistance filter to implement the model of the LRA, in some embodiments, a mathematical equivalent to the LRA may be used in place of the model.

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 electrical or mechanical communication, whether indirectly or directly, with or without intervening elements.

The present disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that a person having ordinary skill in the art would comprehend. Likewise, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that a person having ordinary skill in the art would comprehend where appropriate. Furthermore, in the appended claims reference is made to an apparatus or system, or a component of an apparatus or system, being adapted to, arranged to, capable of, configured to, enabled to, operative to perform a particular function involving said device, system or component, whether or not it or said particular function is activated, turned on or unlocked, provided that said apparatus, system or component is so adapted, arranged, capable of, configured to, enabled, operative or operative. Accordingly, modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, components of the system and apparatus may be integrated or separated. Further, the operations of the systems and devices disclosed herein may be performed by more, fewer, or other components and described methods that may include more, fewer, or other steps. Additionally, the steps may be performed in any suitable order. In this document, "each" refers to each member of a set or each member of a subset of a set.

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

Items depicted in the figures are not necessarily drawn to scale unless specifically noted.

All examples and conditional language recited herein are intended to aid the reader in understanding the present disclosure and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Although the embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and scope of the disclosure.

While specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Moreover, other technical advantages will be apparent to one of ordinary skill in the art upon review of the foregoing figures and description.

To assist the patent office and readers of any patents issued in relation to this application in interpreting the appended claims, applicants desire to note that they do not intend to refer to any appended claims or claim elements as 35u.s.c. § 112(f), unless the word "means for … …" or "step for … …" is specifically used in a particular claim.

Claims

1. A method, comprising:

selecting a selected measurement technique for measuring an impedance of an electromagnetic load from a plurality of impedance measurement techniques based on a state of the electromagnetic load; and

performing the selected measurement technique to generate an estimate of an impedance of the electromagnetic load.

2. The method of claim 1, further comprising, based on the change in state of the electromagnetic load, cyclically selecting the selected measurement technique among the plurality of impedance measurement techniques.

3. The method of claim 1, wherein one of the plurality of impedance measurement techniques comprises applying a pilot driving tone to the electromagnetic load, the pilot driving tone having a frequency substantially higher than a resonant frequency of the electromagnetic load.

4. The method of claim 3, further comprising applying said pilot drive tone prior to playback of a human perceptible effect to said electromagnetic load so that an estimate of the impedance of said electromagnetic load is available prior to playback of a human perceptible effect to said electromagnetic load.

5. The method of claim 4, further comprising applying said pilot driven tone after a triggering event for playback of said human perceptible effect to said electromagnetic load.

6. The method of claim 3, further comprising ramping down the pilot-driven tone to zero at the end of playback of the pilot-driven tone.

7. The method of claim 1, wherein one of the plurality of impedance measurement techniques comprises a thermal model of the electromagnetic load and an elapsed time since a previous estimation of the impedance of the electromagnetic load.

8. The method of claim 7, wherein said thermal model utilizes the time elapsed since said previous estimation to form a new estimate of the impedance prior to playback of the human perceptible effect to said electromagnetic load.

9. The method of claim 8, further comprising estimating an impedance of the electromagnetic load prior to playback of the human perceptible effect to the electromagnetic load and after a triggering event for playback of the human perceptible effect to the electromagnetic load.

10. The method of claim 1, wherein one of the plurality of impedance measurement techniques comprises periodic background calibration of the impedance of the electromagnetic load in the absence of playback of a human perceptible effect to the electromagnetic load for a predetermined period of time.

11. The method of claim 10, further comprising determining an estimate of the impedance of the electromagnetic load from a most recent periodic background calibration estimate of the impedance of the electromagnetic load prior to a triggering event for playback of the human perceptible effect to the electromagnetic load.

12. The method of claim 1, wherein one of the plurality of impedance measurement techniques comprises applying a pilot driving tone to the electromagnetic load, the pilot driving tone having a frequency substantially lower than a resonant frequency of the electromagnetic load.

13. The method of claim 12, further comprising applying an integer number of periods of the pilot driving tone.

14. The method of claim 12, further comprising applying a second pilot driving tone to the electromagnetic load, the second pilot driving tone having a frequency substantially higher than the resonant frequency of the electromagnetic load.

15. The method of claim 14, further comprising tracking an impedance change of the electromagnetic load using the estimate of the impedance of the electromagnetic load formed from the second pilot driver tone before the estimate of the impedance of the electromagnetic load formed from the pilot driver tone is available.

16. The method of claim 12, further comprising applying said pilot driving tone to said electromagnetic load while a human perceptible effect is played back to said electromagnetic load.

17. The method of claim 16, further comprising applying said pilot drive tone and continuously determining an estimate of the impedance of said electromagnetic load for the duration of playback of said human perceptible effect to said electromagnetic load.

18. The method of claim 12, further comprising ramping down the pilot-driven tone to zero at the end of playback of the pilot-driven tone.

19. The method of claim 1, wherein the electromagnetic load comprises a haptic transducer.

20. The method of claim 1, wherein one of the plurality of impedance measurement techniques comprises determining that a playback signal of the electromagnetic load contains sufficient broadband content to obtain an estimate of impedance without requiring additional test stimuli.

21. The method of claim 1, further comprising estimating a sensor offset for sensing a voltage and a current associated with the electromagnetic load while performing the selected measurement technique to generate the estimate of the impedance of the electromagnetic load.

22. A system for estimating an impedance of an electromagnetic load, comprising:

selecting a selected measurement technique for measuring the impedance of the electromagnetic load from a plurality of impedance measurement techniques based on the state of the electromagnetic load; and

23. The system of claim 22, further configured to cycle through the plurality of impedance measurement techniques to select the selected measurement technique based on a change in state of the electromagnetic load.

24. The system of claim 22, wherein one of the plurality of impedance measurement techniques comprises applying a pilot driving tone to the electromagnetic load, the pilot driving tone having a frequency substantially higher than a resonant frequency of the electromagnetic load.

25. The system of claim 24, further configured to apply said pilot drive tone prior to playback of a human perceptible effect to said electromagnetic load, such that an estimate of an impedance of said electromagnetic load is available prior to playback of a human perceptible effect to said electromagnetic load.

26. The system of claim 25, further configured to apply said pilot driven tone after a triggering event for playback of said human perceptible effect to said electromagnetic load.

27. The system of claim 24, further configured to ramp down the pilot-driven tone to zero at the end of playback of the pilot-driven tone.

28. The system of claim 22, wherein one of the plurality of impedance measurement techniques comprises a thermal model of the electromagnetic load and an elapsed time since a previous estimation of the impedance of the electromagnetic load.

29. The system of claim 28, wherein said thermal model utilizes the time elapsed since said previous estimation to form a new estimate of the impedance prior to playback of the human perceptible effect to said electromagnetic load.

30. The system of claim 29, further configured to estimate an impedance of the electromagnetic load prior to playback of the human perceptible effect to the electromagnetic load and after a triggering event for playback of the human perceptible effect to the electromagnetic load.

31. The system of claim 22, wherein one of the plurality of impedance measurement techniques comprises periodic background calibration of the impedance of the electromagnetic load in the absence of playback of a human perceptible effect to the electromagnetic load for a predetermined period of time.

32. The system of claim 31, further configured to determine an estimate of the impedance of the electromagnetic load from a most recent periodic background calibration estimate of the impedance of the electromagnetic load prior to a triggering event for playback of the human perceptible effect to the electromagnetic load.

33. The system of claim 22, wherein one of the plurality of impedance measurement techniques comprises applying a pilot driving tone to the electromagnetic load, the pilot driving tone having a frequency substantially lower than a resonant frequency of the electromagnetic load.

34. The system of claim 33, wherein the system is further configured to apply an integer number of periods of the pilot-driven tone.

35. The system of claim 33, further configured to apply a second pilot driving tone to the electromagnetic load, the second pilot driving tone having a frequency substantially higher than the resonant frequency of the electromagnetic load.

36. The system of claim 35, further configured to track changes in impedance of the electromagnetic load using the estimate of the impedance of the electromagnetic load formed from the second pilot driver tone before the estimate of the impedance of the electromagnetic load formed from the pilot driver tone is available.

37. The system of claim 33, further configured to apply the pilot driver tone to the electromagnetic load while simultaneously playing back a human perceptible effect to the electromagnetic load.

38. The system of claim 37, further configured to apply said pilot driven tone and to continuously determine an estimate of the impedance of said electromagnetic load for the duration of playback of said human perceptible effect to said electromagnetic load.

39. The system of claim 33, further configured to ramp down the pilot-driven tone to zero at the end of playback of the pilot-driven tone.

40. The system of claim 22, wherein the electromagnetic load comprises a haptic transducer.

41. The system of claim 22, wherein one of the plurality of impedance measurement techniques comprises determining that a playback signal of the electromagnetic load contains sufficient broadband content to obtain an estimate of impedance without requiring additional test stimuli.

42. The system of claim 22, further configured to estimate a sensor offset for sensing a voltage and a current associated with the electromagnetic load while performing the selected measurement technique to generate an estimate of an impedance of the electromagnetic load.

43. A master device, comprising:

an electromagnetic load; and

a subsystem coupled to the electromagnetic load and configured to: