Patent Publication Number: US-11662821-B2

Title: In-situ monitoring, calibration, and testing of a haptic actuator

Description:
FIELD OF DISCLOSURE 
     The present disclosure relates in general to in-situ monitoring, calibration, and testing of an electromagnetic transducer, such as a haptic actuator. 
     BACKGROUND 
     Vibro-haptic transducers, for example linear resonant actuators (LRAs), are widely used in portable devices such as mobile phones to generate vibrational feedback to a user. Vibro-haptic feedback in various forms creates different feelings of touch to a user&#39;s skin, and may play increasing roles in human-machine interactions for modern devices. 
     An LRA may be modelled as a mass-spring electro-mechanical vibration system. When driven with appropriately designed or controlled driving signals, an LRA may generate certain desired forms of vibrations. For example, a sharp and clear-cut vibration pattern on a user&#39;s finger may be used to create a sensation that mimics a mechanical button click. This clear-cut vibration may then be used as a virtual switch to replace mechanical buttons. 
       FIG.  1    illustrates an example of a vibro-haptic system in a device  100 . Device  100  may comprise a controller  101  configured to control a signal applied to an amplifier  102 . Amplifier  102  may then drive a vibrational actuator (e.g., haptic transducer)  103  based on the signal. Controller  101  may be triggered by a trigger to output to the signal. The trigger may for example comprise a pressure or force sensor on a screen or virtual button of device  100 . 
     Among the various forms of vibro-haptic feedback, tonal vibrations of sustained duration may play an important role to notify the user of the device of certain predefined events, such as incoming calls or messages, emergency alerts, and timer warnings, etc. In order to generate tonal vibration notifications efficiently, it may be desirable to operate the haptic actuator at its resonance frequency. 
     The resonance frequency f 0  of a haptic transducer may be approximately estimated as: 
                     f   0     =     1     2   ⁢   π   ⁢     CM                 (   1   )               
where C is the compliance of the spring system, and M is the equivalent moving mass, which may be determined based on both the actual moving part in the haptic transducer and the mass of the portable device holding the haptic transducer.
 
     Due to sample-to-sample variations in individual haptic transducers, mobile device assembly variations, temporal component changes caused by aging, and use conditions such as various different strengths of a user gripping of the device, the vibration resonance of the haptic transducer may vary from time to time. 
       FIG.  2    illustrates an example of a linear resonant actuator (LRA) modelled as a linear system. LRAs are non-linear components that may behave differently depending on, for example, the voltage levels applied, the operating temperature, and the frequency of operation. However, these components may be modelled as linear components within certain conditions. In this example, the LRA is modelled as a third order system having 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 force factor of the coil. The driving amplifier outputs the voltage waveform V(t) with the output impedance Ro. The terminal voltage V T (t) may be sensed across the terminals of the haptic transducer. The mass-spring system  201  moves with velocity u(t). 
     A haptic system may require precise control of movements of the haptic transducer. Such control may rely on the magnetic force factor Bl, which may also be known as the electromagnetic transfer function of the haptic transducer. In an ideal case, magnetic force factor Bl can be given by the product B·l, where B is magnetic flux density and l is a total length of electrical conductor within a magnetic field. Both magnetic flux density B and length l should remain constant in an ideal case with motion occurring along a single axis. However, such idealized case does not often represent real-world devices. 
     Instead, magnetic force factor Bl for a haptic transducer is typically nonlinear, non-stationary, temperature-dependent, and has off-axis components of motion that may cause movement in undesired directions and reduce power transfer efficiency of the haptic transducer. The non-idealities may negatively affect haptic transducer performance, which may in turn translate into unsatisfactory customer experience. 
     SUMMARY 
     In accordance with the teachings of the present disclosure, the disadvantages and problems associated with existing approaches for characterizing non-idealities of an electromagnetic transducer may be reduced or eliminated. 
     In accordance with embodiments of the present disclosure, a method may include measuring an electrical parameter of an electromagnetic load having a moving mass during the absence of a driving signal actively driving the electromagnetic load, measuring a mechanical parameter of mechanical motion of a host device comprising the electromagnetic load, correlating a relationship between the mechanical parameter and the electrical parameter, and calibrating the electromagnetic load across a plurality of mechanical motion conditions based on the relationship. 
     In accordance with these and other embodiments of the present disclosure, a system may include a first input for measuring an electrical parameter of an electromagnetic load having a moving mass during the absence of a driving signal actively driving the electromagnetic load, a second input for measuring a mechanical parameter of mechanical motion of a host device comprising the electromagnetic load, and a processing subsystem configured to correlate a relationship between the mechanical parameter and the electrical parameter and calibrate the electromagnetic load across a plurality of mechanical motion conditions based on the relationship. 
     In accordance with these and other embodiments of the present disclosure, a host device may include an electromagnetic load and a processing subsystem configured to measure an electrical parameter of an electromagnetic load having a moving mass during the absence of a driving signal actively driving the electromagnetic load, measure a mechanical parameter of mechanical motion of a host device comprising the electromagnetic load, correlate a relationship between the mechanical parameter and the electrical parameter, and calibrate the electromagnetic load across a plurality of mechanical motion conditions based on the relationship. 
     Technical advantages of the present disclosure may be readily apparent to one having ordinary skill in the art from the figures, description and claims included herein. The objects and advantages of the embodiments will be realized and achieved at least by the elements, features, and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are examples and explanatory and are not restrictive of the claims set forth in this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE 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    illustrates an example of a vibro-haptic system in a device, as is known in the art; 
         FIG.  2    illustrates an example of a Linear Resonant Actuator (LRA) modelled as a linear system, as is known in the art; 
         FIG.  3    illustrates selected components of an example host device incorporating force sensing using an electromagnetic load of the host device, in accordance with embodiments of the present disclosure; and 
         FIG.  4    illustrates a flow chart of an example method for in-situ monitoring, calibration, and testing of an electromagnetic transducer, in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The description below sets forth example embodiments according to this disclosure. Further example embodiments and implementations will be apparent to those having ordinary skill in the art. Further, those having ordinary skill in the art will recognize that various equivalent techniques may be applied in lieu of, or in conjunction with, the embodiment discussed below, and all such equivalents should be deemed as being encompassed by the present disclosure. 
     Various electronic devices or smart devices may have transducers, speakers, and acoustic output transducers, for example any transducer for converting a suitable electrical driving signal into an acoustic output such as a sonic pressure wave or mechanical vibration. For example, many electronic devices may include one or more speakers or loudspeakers for sound generation, for example, for playback of audio content, voice communications and/or for providing audible notifications. 
     Such speakers or loudspeakers may comprise an electromagnetic actuator, for example a voice coil motor, which is mechanically coupled to a flexible diaphragm, for example a conventional loudspeaker cone, or which is mechanically coupled to a surface of a device, for example the glass screen of a mobile device. Some electronic devices may also include acoustic output transducers capable of generating ultrasonic waves, for example for use in proximity detection type applications and/or machine-to-machine communication. 
     Many electronic devices may additionally or alternatively include more specialized acoustic output transducers, for example, haptic transducers, tailored for generating vibrations for haptic control feedback or notifications to a user. Additionally or alternatively, an electronic device may have a connector, e.g., a socket, for making a removable mating connection with a corresponding connector of an accessory apparatus, and may be arranged to provide a driving signal to the connector so as to drive a transducer, of one or more of the types mentioned above, of the accessory apparatus when connected. Such an electronic device will thus comprise driving circuitry for driving the transducer of the host device or connected accessory with a suitable driving signal. For acoustic or haptic transducers, the driving signal may generally be an analog time varying voltage signal, for example, a time varying waveform. 
       FIG.  3    illustrates selected components of an example host device  300  incorporating force sensing using an electromagnetic load  301  of host device  300 , in accordance with embodiments of the present disclosure. Host device  300  may include, without limitation, a mobile device, home application, a vehicle, and/or any other system, device, or apparatus that includes a human-machine interface. Electromagnetic load  301  may include any suitable load with a complex impedance, including without limitation a haptic transducer, a loudspeaker, a microspeaker, a piezoelectric transducer, or other suitable transducer. 
     In operation, a signal generator  324  of a processing subsystem  305  of host device  300  may generate a raw transducer driving signal x′(t) (which, in some embodiments, may be a waveform signal, such as a haptic waveform signal or audio signal). Raw transducer driving signal x′(t) may be generated based on a desired playback waveform received by signal generator  324 . 
     Raw transducer driving signal x′(t) may be received by compensation filter  326  which, as described in greater detail below, may be applied to raw transducer driving signal x′(t) to compensate for non-idealities of electromagnetic load  301  in order to generate compensated transducer driving signal x(t). 
     Compensated transducer driving signal x(t) may in turn be amplified by amplifier  306  to generate a driving signal V(t) for driving electromagnetic load  301 . Responsive to driving signal V(t), a sensed terminal voltage V T (t) of electromagnetic load  301  may be converted to a digital representation by a first analog-to-digital converter (ADC)  303 . Similarly, sensed current I(t) may be converted to a digital representation by a second ADC  304 . Current I(t) may be sensed across a shunt resistor  302  having resistance R s  coupled to a terminal of electromagnetic load  301 . The terminal voltage V T (t) may be sensed by a terminal voltage sensing block  307 , for example a volt-meter. 
     As shown in  FIG.  3   , processing subsystem  305  may include a back-EMF estimate block  308  that may estimate back-EMF voltage V B (t). In general, back-EMF voltage V B (t) may not be directly measured from outside of the haptic transducer. However, the terminal voltage V T (t) measured at the terminals of the haptic transducer may be related to V B (t) by: 
                       V   T     ⁡     (   t   )       =         V   B     ⁡     (   t   )       +     Re   ·     I   ⁡     (   t   )         +     Le   ·       d   ⁢           ⁢     I   ⁡     (   t   )           d   ⁢           ⁢   t                   (   2   )               
where the parameters are defined as described with reference to  FIG.  2   . Consequently, back-EMF voltage V B (t) may be estimated according to equation (2) which may be rearranged as:
 
                       V   B     ⁡     (   t   )       =         V   T     ⁡     (   t   )       -     Re   ·     I   ⁡     (   t   )         -     Le   ⁢       d   ⁢           ⁢     I   ⁡     (   t   )           d   ⁢           ⁢   t                   (   3   )               
Because back-EMF voltage V B (t) may be proportional to velocity of the moving mass of electromagnetic load  301 , back-EMF voltage V B (t) may in turn provide an estimate of such velocity.
 
     In some embodiments, back-EMF estimate block  308  may be implemented as a digital filter with a proportional and parallel difference path. The estimates of DC resistance Re and inductance Le may not need to be accurate (e.g., within an approximate 10% error may be acceptable), and thus, fixed values from an offline calibration or from a data sheet specification may be sufficient. As an example, in some embodiments, back-EMF estimate block  308  may determine estimated back-EMF voltage V B (t) in accordance with the teachings of U.S. patent application Ser. No. 16/559,238, filed Sep. 3, 2019, which is incorporated by reference herein in its entirety. 
     Based on such estimated back-EMF voltage V B (t) and measurements of velocity and/or acceleration from an inertial measurement unit  312 , an in-situ characterization subsystem  310  may, as described in greater detail below, calculate and store empirical measurements for magnetic force factor Bl, which in turn may be used to generate compensation parameters for controlling a response of compensation filter  326 . 
     Inertial measurement unit  312  may comprise any suitable system, device, or apparatus configured to sense one or parameters related to motion of host device  300 , for example velocity and/or acceleration, and generate one or more signals indicative of such one or more measured parameters. For example, inertial measurement unit  312  may include one or more accelerometers, gyroscopes, and magnetometers. In some embodiments, inertial measurement unit  312  may include six axes of measurement, thus allowing for sensing of velocity, acceleration, or other parameters related to motion of host device  300 . 
     The relationship among estimated back-EMF voltage V B (t), magnetic force factor Bl, and an estimated velocity u(t) of a moving mass of electromagnetic load  301  may be determined from the relationship:
 
 V   B ( t )= Bl·u ( t )
 
     Thus, in the absence of a playback waveform received by signal generator  324 , when host device  300  is moved (e.g., by an end user thereof), inertial measurement unit  312  may measure velocity u(t). Accordingly, by knowing measured velocity u(t) and estimated back-EMF voltage V B (t), in-situ characterization subsystem  310  may allow for calculation of magnetic force factor Bl specific to the observed velocity. For example, if estimated back-EMF voltage V B (t) is measured to be 80 millivolts at a velocity of 0.1 meters per second of the moving mass of electromagnetic load  301 , then in-situ characterization subsystem  310  may determine a magnetic force factor Bl equal to 0.8 Tesla-meters for electromagnetic load  301  at a velocity of 0.1 meters per second. 
     It is noted that this calculation relies on treating host device  300  as a high-impedance velocity source to the mass-spring system of electromagnetic load  301 . Such convention may be known in the art as “supercompliance” and the use of such convention herein may be justified where a high ratio exists between the mass of host device  300  to the mass of the moving mass of electromagnetic load  301 . In addition or alternatively, host device  300  may be driven by an external velocity source capable of producing the force necessary to achieve a velocity to the mass-spring system of electromagnetic load  301 . 
     Over time during its operation, in-situ characterization subsystem  310  may create a library of magnetic force factor Bl measurements at various velocities, providing a complete operational space of magnetic force factor Bl in three dimensions of velocity space. Accordingly, in-situ characterization subsystem  310  may, based on the characterization of magnetic force factor Bl at various velocities, generate and communicate to compensation filter  326  one or more control signals in the form of compensation parameters in order to control a response of compensation filter  326  to compensate for non-idealities of electromagnetic load  301 , including non-linearity and other non-idealities of magnetic force factor Bl. 
     Such continuous collection of data may also enable in-situ characterization subsystem  310  to perform diagnostics based on changes in magnetic force factor Bl over time. For example, threshold values for changes in magnetic force factor Bl over time may be used to trigger alerts to an end user and/or other remedial actions. 
     In some embodiments, in-situ characterization subsystem  310  may perform its functionality during normal use of host device  300  by an end user, which may be referred to as real-time or field calibration, in which the end user (e.g., intentionally or incidentally) supplies the motion to host device  300 . In these and other embodiments, in-situ characterization subsystem  310  may perform its functionality during post-production calibration, in which motion may be controlled by a mechanical exciter of a test/calibration system. 
       FIG.  4    illustrates a flow chart of an example method  400  for in-situ monitoring, calibration, and testing of an electromagnetic transducer, in accordance with embodiments of the present disclosure. According to some embodiments, method  400  may begin at step  402 . As noted above, teachings of the present disclosure may be implemented in a variety of configurations of host device  300 . As such, the preferred initialization point for method  400  and the order of the steps comprising method  400  may depend on the implementation chosen. 
     At step  402 , in-situ characterization subsystem  310  may determine if a playback waveform is being input to signal generator  324 . If a playback waveform is being input to signal generator  324 , method  400  may proceed to step  404 . Otherwise, method  400  may proceed to step  406 . 
     At step  404 , responsive to determining that a playback waveform is being input to signal generator  324 , in-situ characterization subsystem  310  may freeze characterization and the response of compensation filter  326  may be based on existing compensation parameters generated from existing characterizations of magnetic force factor Bl. After completion of step  404 , method  400  may return again to step  402 . 
     At step  406 , responsive to an absence of a playback waveform being input to signal generator  324 , in-situ characterization subsystem  310  may receive measurements for estimated back-EMF voltage V B (t) from back-EMF estimate block  308  and one or more measured parameters related to motion of host device  300  from inertial measurement unit  312 , including velocity u(t). 
     At step  408 , in-situ characterization subsystem  310  may, based on measurements of estimated back-EMF voltage V B (t) and velocity u(t), calculate associated magnetic force factors Bl and associate each of a plurality of measured velocities u(t) to a respective magnetic force factor Bl calculated for each velocity u(t), and store such mappings of velocities u(t) to respective magnetic force factors Bl (e.g., in computer-readable media integral to host device  300  and accessible by in-situ characterization subsystem  310 ). 
     At step  410 , in-situ characterization subsystem  310  may update compensation parameters communicated to compensation filter  326  based on newly calculated magnetic force factors Bl as a function of velocity u(t). After completion of step  410 , method  400  may proceed again to step  402 . 
     Although  FIG.  4    discloses a particular number of steps to be taken with respect to method  400 , method  400  may be executed with greater or fewer steps than those depicted in  FIG.  4   . In addition, although  FIG.  4    discloses a certain order of steps to be taken with respect to method  400 , the steps comprising method  400  may be completed in any suitable order. 
     Method  400  may be implemented in whole or part using host device  300  and/or any other system operable to implement method  400 . In certain embodiments, method  400  may be implemented partially or fully in software and/or firmware embodied in computer-readable media. 
     As used herein, when two or more elements are referred to as “coupled” to one another, such term indicates that such two or more elements are in electronic communication or mechanical communication, as applicable, whether connected indirectly or directly, with or without intervening elements. 
     This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, 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, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set. 
     Although exemplary embodiments are illustrated in the figures 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 in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described above. 
     Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale. 
     All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the disclosure and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure. 
     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 readily apparent to one of ordinary skill in the art after review of the foregoing figures and description. 
     To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke 35 U.S.C. § 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim.