Patent Publication Number: US-10782785-B2

Title: Vibro-haptic design and automatic evaluation of haptic stimuli

Description:
RELATED APPLICATION 
     The present disclosure claims priority to U.S. Provisional Patent Application Ser. No. 62/623,156, filed Jan. 29, 2018, which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF DISCLOSURE 
     The present disclosure relates in general to electronic devices with user interfaces, (e.g., mobile devices, game controllers, instrument panels, etc.), and more particularly, a haptic system for use in a system for mechanical button replacement in a mobile device, for use in haptic feedback for capacitive sensors, and/or other suitable applications. 
     BACKGROUND 
     Linear resonant actuators (LRAs) and other vibrational actuators (e.g., rotational actuators, vibrating motors, etc.) are increasingly being used in mobile devices (e.g., mobile phones, personal digital assistants, video game controllers, etc.) to generate vibrational feedback for user interaction with such devices. Typically, a force/pressure sensor detects user interaction with the device (e.g., a finger press on a virtual button of the device) and in response thereto, the linear resonant actuator vibrates to provide feedback to the user. For example, a linear resonant actuator may vibrate in response to force to mimic to the user the feel of a mechanical button click. 
     With appropriate design of input signal to an LRA, certain forms of vibration patterns may be generated, and specific haptic effects may be perceived by a user. Among such haptic application scenarios, one important type of haptic notification is generation of a button click (or virtual switch) effect, in which natural, sharp, and clear-cut haptic perceptions generated by the LRA that mimic the clicks of a true mechanical button are desirable. 
     From a haptic waveform received at its input, an LRA transducer may create a main pulse of vibrations on a device, followed by a tail of residual resonant vibrations of certain length, depending on characteristics of input haptic waveform stimulus together with the vibrational properties of the LRA. To achieve sharp and clear-cut haptic perceptions on a user&#39;s fingers and/or palm, it is important to appropriately design the waveform stimulus input to the LRA, so that the vibration pulses felt by the user satisfy certain time and frequency patterns (e.g., within a certain time duration range) and do not have prolonged resonating tails. A feedback vibration pattern with either too long a main pulse or with excessive duration in resonating tails may deteriorate the sharpness and clarity (or “crispness”) of the haptic feeling on the fingertip and/or palm, and may render the perception to have prolonged ringing, which is far less pleasant compared to the natural and crisp perceptions typically generated by a well-designed conventional mechanical button. 
     Accordingly, measures for evaluation of perceived haptic effects are desired. Subjective evaluations, e.g., manual haptic scoring by human subjects on device under test (DUT), is one potential method. Subjective scoring has the advantage in that it directly describes human perception. However, subjective evaluations also demonstrate disadvantages, such as being more expensive in cost and involving higher time consumption, less efficiency, and potential variations due to differing human subjectivity and perception. 
     Several objective evaluation measures already exist for the characterization of haptic performances based on the analysis of measurement of a vibrational signal waveform. Some examples of objective measures, which provide different perspectives in the objective description of vibro-haptic performance of virtual mechanical button clicks generated by an LRA upon a given stimulus signal, may include: 
     1) Peak or root-mean-square (RMS) vibration level (e.g., stated in units of acceleration), in the form of maximum acceleration peak value, may describe the maximum intensity, or strength, of a vibration generated by an LRA. Such measure may provide a coarse estimate of strength of the energy of a haptic response. An actual human perception of the strength may deviate from this value, depending on the actual characteristics of the vibrational pulse. 
     2) Attack time (e.g., stated in milliseconds) may describe a latency from a start of a response stimulus to the time when the vibration level reaches 90% of the above mentioned peak level. Such measure may quantify how fast a haptic click happens and achieves its maximum strength. 
     3) Decay time (e.g., stated in milliseconds) may describe a latency from the time of peak vibration to the time when the vibration level drops below 10% of the peak vibration level. It tells how fast the haptic vibration decays in energy, but not necessarily in haptic-perceivable energy. 
     These objective measures are computationally simple and robust, and have already found applications in LRA component and system evaluations and specifications. However, they fail to provide a subjectively reliable measure that is relevant to subjective human haptic perceptions, and thus objective measures to reliably measure subjective perceptions are desired. 
     SUMMARY 
     In accordance with the teachings of the present disclosure, the disadvantages and problems associated with generating haptic feedback in a mobile device may be reduced or eliminated. 
     In accordance with embodiments of the present disclosure, a method for quantifying fidelity of a haptic signal may include receiving a response signal indicative of a vibrational response of a vibrational transducer to a haptic playback waveform driven to the vibrational transducer, perceptually filtering the response signal to obtain human haptic-perceptible components of the response signal, and quantifying fidelity of the haptic playback waveform based on at least one quantitative characteristic of the human haptic-perceptible components of the response signal. 
     In accordance with embodiments of the present disclosure, a system for quantifying fidelity of a haptic signal may include an input configured to receive a response signal indicative of a vibrational response of a vibrational transducer to a haptic playback waveform driven to the vibrational transducer and a processor configured to perceptually filter the response signal to obtain human haptic-perceptible components of the response signal and quantify fidelity of the haptic playback waveform based on at least one quantitative characteristic of the human haptic-perceptible components of the response signal. 
     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 a block diagram of selected components of an example mobile device, in accordance with embodiments of the present disclosure; 
         FIG. 2  illustrates a block diagram of selected components of an example integrated haptic system, in accordance with embodiments of the present disclosure; 
         FIG. 3  illustrates a block diagram of selected components of an example processing system for use in the integrated haptic system of  FIG. 2 , in accordance with embodiments of the present disclosure; 
         FIG. 4  illustrates a block diagram of selected components of an example test system for evaluation of haptic stimuli for use in design of haptic waveforms and haptic devices, in accordance with embodiments of the present disclosure; 
         FIG. 5  illustrates a flow chart of an example method for determination of a perceived-haptic sharpness measure, in accordance with embodiments of the present disclosure; 
         FIG. 6A  illustrates an example haptic playback waveform a(t), in accordance with embodiments of the present disclosure; 
         FIG. 6B  illustrates an example acceleration response signal measured in response to the example haptic playback waveform shown in  FIG. 6A , in accordance with embodiments of the present disclosure; 
         FIG. 7  illustrates an example of a haptic perceptual threshold curve, in accordance with embodiments of the present disclosure; 
         FIG. 8  illustrates a flow chart of an example method for automatic evaluation and design of haptic stimuli, in accordance with embodiments of the present disclosure; and 
         FIG. 9  illustrates an example of a haptic sharpness diagram, in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a block diagram of selected components of an example mobile device  102 , in accordance with embodiments of the present disclosure. As shown in  FIG. 1 , mobile device  102  may comprise an enclosure  101 , a controller  103 , a memory  104 , a force sensor  105 , a microphone  106 , a linear resonant actuator  107 , a radio transmitter/receiver  108 , a speaker  110 , and an integrated haptic system  112 . 
     Enclosure  101  may comprise any suitable housing, casing, or other enclosure for housing the various components of mobile device  102 . Enclosure  101  may be constructed from plastic, metal, and/or any other suitable materials. In addition, enclosure  101  may be adapted (e.g., sized and shaped) such that mobile device  102  is readily transported on a person of a user of mobile device  102 . Accordingly, mobile device  102  may include but is not limited to a smart phone, a tablet computing device, a handheld computing device, a personal digital assistant, a notebook computer, a video game controller, or any other device that may be readily transported on a person of a user of mobile device  102 . 
     Controller  103  may be housed within enclosure  101  and may include any system, device, or apparatus configured to interpret and/or execute program instructions and/or process data, and may include, without limitation 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, controller  103  interprets and/or executes program instructions and/or processes data stored in memory  104  and/or other computer-readable media accessible to controller  103 . 
     Memory  104  may be housed within enclosure  101 , may be communicatively coupled to controller  103 , and may include any system, device, or apparatus configured to retain program instructions and/or data for a period of time (e.g., computer-readable media). Memory  104  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 storage, opto-magnetic storage, or any suitable selection and/or array of volatile or non-volatile memory that retains data after power to mobile device  102  is turned off. 
     Microphone  106  may be housed at least partially within enclosure  101 , may be communicatively coupled to controller  103 , and may comprise any system, device, or apparatus configured to convert sound incident at microphone  106  to an electrical signal that may be processed by controller  103 , wherein such sound is converted to an electrical signal using a diaphragm or membrane having an electrical capacitance that varies as based on sonic vibrations received at the diaphragm or membrane. Microphone  106  may include an electrostatic microphone, a condenser microphone, an electret microphone, a microelectromechanical systems (MEMs) microphone, or any other suitable capacitive microphone. 
     Radio transmitter/receiver  108  may be housed within enclosure  101 , may be communicatively coupled to controller  103 , and may include any system, device, or apparatus configured to, with the aid of an antenna, generate and transmit radio-frequency signals as well as receive radio-frequency signals and convert the information carried by such received signals into a form usable by controller  103 . Radio transmitter/receiver  108  may be configured to transmit and/or receive various types of radio-frequency signals, including without limitation, 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  110  may be housed at least partially within enclosure  101  or may be external to enclosure  101 , may be communicatively coupled to controller  103 , and may comprise any system, device, or apparatus configured to produce sound in response to electrical audio signal input. In some embodiments, a speaker may comprise a dynamic loudspeaker, which employs a lightweight diaphragm mechanically coupled to a rigid frame via a flexible suspension that constrains a voice coil to move axially through a cylindrical magnetic gap. When an electrical signal is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the driver&#39;s magnetic system interact, generating a mechanical force that causes the coil (and thus, the attached cone) to move back and forth, thereby reproducing sound under the control of the applied electrical signal coming from the amplifier. 
     Force sensor  105  may be housed within enclosure  101 , and may include any suitable system, device, or apparatus for sensing a force, a pressure, or a touch (e.g., an interaction with a human finger) and generating an electrical or electronic signal in response to such force, pressure, or touch. In some embodiments, such electrical or electronic signal may be a function of a magnitude of the force, pressure, or touch applied to the force sensor. In these and other embodiments, such electronic or electrical signal may comprise a general purpose input/output signal (GPIO) associated with an input signal to which haptic feedback is given (e.g., a capacitive touch screen sensor or other capacitive sensor to which haptic feedback is provided). For purposes of clarity and exposition in this disclosure, the term “force” as used herein may refer not only to force, but to physical quantities indicative of force or analogous to force, such as, but not limited to, pressure and touch. 
     Linear resonant actuator  107  may be housed within enclosure  101 , and may include any suitable system, device, or apparatus for producing an oscillating mechanical force across a single axis. For example, in some embodiments, linear resonant actuator  107  may rely on an alternating current voltage to drive a voice coil pressed against a moving mass connected to a spring. When the voice coil is driven at the resonant frequency of the spring, linear resonant actuator  107  may vibrate with a perceptible force. Thus, linear resonant actuator  107  may be useful in haptic applications within a specific frequency range. While, for the purposes of clarity and exposition, this disclosure is described in relation to the use of linear resonant actuator  107 , it is understood that any other type or types of vibrational actuators (e.g., eccentric rotating mass actuators) may be used in lieu of or in addition to linear resonant actuator  107 . In addition, it is also understood that actuators arranged to produce an oscillating mechanical force across multiple axes may be used in lieu of or in addition to linear resonant actuator  107 . As described elsewhere in this disclosure, a linear resonant actuator  107 , based on a signal received from integrated haptic system  112 , may render haptic feedback to a user of mobile device  102  for at least one of mechanical button replacement and capacitive sensor feedback. 
     Integrated haptic system  112  may be housed within enclosure  101 , may be communicatively coupled to force sensor  105  and linear resonant actuator  107 , and may include any system, device, or apparatus configured to receive a signal from force sensor  105  indicative of a force applied to mobile device  102  (e.g., a force applied by a human finger to a virtual button of mobile device  102 ) and generate an electronic signal for driving linear resonant actuator  107  in response to the force applied to mobile device  102 . Detail of an example integrated haptic system in accordance with embodiments of the present disclosure is depicted in  FIG. 2 . 
     Although specific example components are depicted above in  FIG. 1  as being integral to mobile device  102  (e.g., controller  103 , memory  104 , force sensor  105 , microphone  106 , radio transmitter/receiver  108 , speakers(s)  110 ), a mobile device  102  in accordance with this disclosure may comprise one or more components not specifically enumerated above. For example, although  FIG. 1  depicts certain user interface components, mobile device  102  may include one or more other user interface components in addition to those depicted in  FIG. 1 , including but not limited to a keypad, a touch screen, and a display, thus allowing a user to interact with and/or otherwise manipulate mobile device  102  and its associated components. 
       FIG. 2  illustrates a block diagram of selected components of an example integrated haptic system  112 , in accordance with embodiments of the present disclosure. In some embodiments, integrated haptic system  112  may be used to implement integrated haptic system  112  of  FIG. 1 . Although  FIG. 2  depicts an example of an integrated haptic system, other implementations for a haptic system may be used, including without limitation those implementations described in U.S. patent application Ser. No. 15/722,128 entitled “Integrated Haptic System,” and filed Oct. 2, 2017, which is incorporated by reference herein in its entirety. 
     As shown in  FIG. 2 , integrated haptic system  112  may include a digital signal processor (DSP)  202 , a memory  204 , and an amplifier  206 . DSP  202  may include any system, device, or apparatus configured to interpret and/or execute program instructions and/or process data. In some embodiments, DSP  202  may interpret and/or execute program instructions and/or process data stored in memory  204  and/or other computer-readable media accessible to DSP  202 . 
     Memory  204  may be communicatively coupled to DSP  202 , and may include any system, device, or apparatus configured to retain program instructions and/or data for a period of time (e.g., computer-readable media). Memory  204  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 storage, opto-magnetic storage, or any suitable selection and/or array of volatile or non-volatile memory that retains data after power to mobile device  102  is turned off. 
     Amplifier  206  may be electrically coupled to DSP  202  and may comprise any suitable electronic system, device, or apparatus configured to increase the power of an input signal V IN  (e.g., a time-varying voltage or current) to generate an output signal V OUT . For example, amplifier  206  may use electric power from a power supply (not explicitly shown) to increase the amplitude of a signal. Amplifier  206  may include any suitable amplifier class, including without limitation, a Class-D amplifier. 
     In operation, memory  204  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  107 ) as a function of time. DSP  202  may be configured to receive a force signal V SENSE  from force sensor  105  indicative of force applied to force sensor  105 . Either in response to receipt of force signal V SENSE  indicating a sensed force or independently of such receipt, DSP  202  may retrieve a haptic playback waveform from memory  204  and process such haptic playback waveform to determine a processed haptic playback signal V IN . In embodiments in which amplifier  206  is a Class D amplifier, processed haptic playback signal V IN  may comprise a pulse-width modulated signal. In response to receipt of force signal V SENSE  indicating a sensed force, DSP  202  may cause processed haptic playback signal V IN  to be output to amplifier  206 , and amplifier  206  may amplify processed haptic playback signal V IN  to generate a haptic output signal V OUT  for driving linear resonant actuator  107 . Detail of an example processing system implemented by DSP  202  is depicted in  FIG. 3 . 
     In some embodiments, integrated haptic system  112  may be formed on a single integrated circuit, thus enabling lower latency than existing approaches to haptic feedback control. By providing integrated haptic system  112  as part of a single monolithic integrated circuit, latencies between various interfaces and system components of integrated haptic system  112  may be reduced or eliminated. 
     As shown in  FIG. 3 , DSP  202  may receive diagnostic inputs from which processing system  300  may monitor and adjust operation of amplifier  206  in response thereto. For example, as discussed below with respect to  FIG. 3 , DSP  202  may receive measurements from linear resonant actuator  107  to estimate the vibrational transfer function of linear resonant actuator  107 . However, in some embodiments, DSP  202  may receive and monitor one or more other diagnostic inputs, and DSP  202  may control operation of amplifier  206  in response thereto. For example, in some embodiments, DSP  202  may monitor a current level associated with linear resonant actuator  107  and/or a voltage level associated with linear resonant actuator  107 . From such measurements, DSP  202  may be able to infer or calculate a status (e.g., status of motion) of linear resonant actuator  107 . For example, from a monitored voltage and current, DSP  202  may be able to employ a mathematical model of linear resonant actuator  107  to estimate a displacement, velocity, and/or acceleration of linear resonant actuator  107 . As another example, DSP  202  may inject a high-frequency signal into linear resonant actuator  107  and infer an inductance of linear resonant actuator  107  based on the current and/or voltage responses of linear resonant actuator  107  to the injected signal. From the inductance, DSP  202  may be able to estimate a displacement of linear resonant actuator  107 . Based on determined status information (e.g., displacement, velocity, and/or acceleration), DSP  202  may control processed haptic playback signal V IN  for any suitable purpose, including protecting linear resonant actuator  107  from over-excursion that could lead to damage to linear resonant actuator  107  or other components of mobile device  102 . As yet another example, one or more diagnostic inputs may be monitored to determine an operational drift of linear resonant actuator  107 , and DSP  202  may control amplifier  206  and/or processed haptic playback signal V IN  in order to account for the operational drift. As a further example, one or more diagnostic inputs may be monitored to determine temperature effects of linear resonant actuator  107  (e.g., thermally induced changes in the performance of linear resonant actuator  107 ), and DSP  202  may control amplifier  206  and/or processed haptic playback signal V IN  in order to account for the temperature effects. 
       FIG. 3  illustrates a block diagram of selected components of an example processing system  300  implemented by DSP  202 , in accordance with embodiments of the present disclosure. As shown in  FIG. 3 , processing system  300  may include vibrational pulse processing  302 , regulated inversion  304 , click-driving pulse processing  306 , a comparator  308 , and vibrational transfer function estimation  310 . In operation, vibrational pulse processing  302  may receive a haptic playback waveform a(t) (or relevant parameters of such a waveform such as frequency and duration) and process such waveform to generate an intermediate signal a 1 (t). Processing performed by vibrational pulse processing  302  may include, without limitation, filtering (e.g., band-pass filtering) for frequency bands of interest, equalization of haptic playback waveform a(t) to obtain a desired spectral shape, and/or temporal truncation or extrapolation of haptic playback waveform a(t). By adjusting or tuning the temporal duration and frequency envelope of haptic playback waveform a(t), various haptic feelings as perceived by a user and/or audibility of the haptic response may be achieved. 
     Regulated inversion  304  may apply an inverse transfer function ITF to intermediate signal a 1 (t), either in the frequency domain or equivalently in the time domain through inverse filtering. Such inverse transfer function ITF may be generated from vibrational transfer function estimation  310  based on actual vibrational measurements of linear resonant actuator  107  and/or model parameters of linear resonant actuator  107 . Inverse transfer function ITF may be the inverse of a transfer function that correlates output voltage signal V OUT  to actual acceleration of linear resonant actuator  107 . By applying inverse transfer function ITF to intermediate signal a 1 (t), regulated inversion  304  may generate an inverted vibration signal V INT  in order to apply inversion to specific target vibrational click pulses to obtain an approximation of certain desired haptic click signals to drive the vibrational actuators for the generation of haptic clicks. In embodiments in which inverse transfer function ITF is calculated based on measurements of linear resonant actuator  107 , processing system  300  may implement a closed-loop feedback system for generating output signal V OUT , such that processing system  300  may track vibrational characteristics of linear resonant actuator  107  over the lifetime of linear resonant actuator  107  to enable more accurate control of the haptic response generated by integrated haptic system  112 . 
     In some embodiments, processing system  300  may not employ an adaptive inverse transfer function ITF, and instead apply a fixed inverse transfer function ITF. In yet other embodiments, the haptic playback waveforms a(t) stored in memory  204  may include waveforms already adjusted by a fixed inverse transfer function ITF, in which case processing system  300  may not include blocks  302  and  304 , and haptic playback waveforms a(t) may be fed directly to click-driving pulse processing block  306 . 
     Click-driving pulse processing  306  may receive inverted vibration signal V INT  and control resonant tail suppression of inverted vibration signal V INT  in order to generate processed haptic playback signal V IN . Processing performed by click-driving pulse processing  306  may include, without limitation, truncation of inverted vibration signal V INT , minimum phase component extraction for inverted vibration signal V INT , and/or filtering to control audibility of haptic playback signal V IN . 
     Comparator  308  may compare a digitized version of force signal V SENSE  to a signal threshold V TH  related to a threshold force, and responsive to force signal V SENSE  exceeding signal threshold V TH , may enable haptic playback signal V IN  to be communicated to amplifier  206 , such that amplifier  206  may amplify haptic playback signal V IN  to generate output signal V OUT . 
     Although  FIG. 3  depicts comparator  308  as a simple analog comparator, in some embodiments, comparator  308  may include more detailed logic and/or comparison than shown in  FIG. 3 , with the enable signal ENABLE output by comparator  308  depending on one or more factors, parameters, and/or measurements in addition to in or lieu of comparison to a threshold force level. 
     In addition, although  FIG. 3  depicts enable signal ENABLE being communicated to click-driving pulse processing  306  and selectively enabling/disabling haptic playback signal V IN , in other embodiments, enable signal ENABLE may be communicated to another component of processing system  300  (e.g., vibrational pulse processing  302 ) in order to enable, disable, or otherwise condition an output of such other component. 
     As noted above with regard to the description of  FIG. 2 , integrated haptic system  112  may include memory  204  for storing input haptic waveforms for input to linear resonant actuator  107  (e.g., after processing by DSP  202  and amplification by amplifier  206 ). However, as noted in the Background section of this application, determination of the one or more specific haptic waveforms to store in memory  204  may be critical to generation of a pleasing or otherwise desirable haptic response by linear resonant actuator  107 . To that end,  FIG. 4  illustrates a block diagram of selected components of an example test system  400  for evaluation of haptic stimuli for use in design of haptic waveforms and haptic devices, in accordance with embodiments of the present disclosure. As shown in  FIG. 4 , example test system  400  may include a processor  402 , a memory  404 , an amplifier  406 , a linear resonant actuator  107  as a device under test, and an accelerometer  412 . 
     Processor  402  may include any system, device, or apparatus configured to interpret and/or execute program instructions and/or process data, and may include, without limitation 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, processor  402  may interpret and/or execute program instructions and/or process data stored in memory  404  and/or other computer-readable media accessible to processor  402 , as described in greater detail below. 
     Memory  404  may be communicatively coupled to processor  402 , and may include any system, device, or apparatus configured to retain program instructions and/or data for a period of time (e.g., computer-readable media). Memory  404  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 storage, opto-magnetic storage, or any suitable selection and/or array of volatile or non-volatile memory that retains data after power to test system  400  is turned off. As shown in  FIG. 4 , memory  404  may include test module  408  and candidate waveforms  410 . 
     Test module  408  may comprise a program of executable instructions that may be read and executed by processor  402  to carry out some or all of the functionality of test system  400 , as described in greater detail below. 
     Candidate waveforms  410  may comprise 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  107 ) as a function of time. In operation, as described in greater detail below, test module  408  executing on processor  402  may evaluate the one or more candidate waveforms  410  to provide an objective measure of user-perceived haptic sensation by applying a candidate waveform  410  to the input of linear resonant actuator  107  and analyzing an acceleration response signal x(t) generated by accelerometer  412 . 
     Amplifier  406  may be electrically coupled to processor  402  and may comprise any suitable electronic system, device, or apparatus configured to increase the power of an input signal (e.g., a(t), represented as a time-varying voltage or current) to generate an output signal (e.g., a′(t), represented as a time-varying voltage or current). For example, amplifier  406  may use electric power from a power supply (not explicitly shown) to increase the amplitude of a signal. Amplifier  406  may include any suitable amplifier class, including without limitation, a Class-D amplifier. In some embodiments, amplifier  406  may be identical or substantially similar to amplifier  206  of integrated haptic system  112 . 
     Accelerometer  412  may be communicatively coupled to processor  402 , and may include any system, device, or apparatus configured to measure an acceleration (e.g., proper acceleration) generated by linear resonant actuator  107  and generate an acceleration response signal x(t) indicative of such measured acceleration. 
       FIG. 5  illustrates a flow chart of an example method  500  for determination of a perceived haptic sharpness measure that may take into account the properties of human vibro-haptic (or vibro-tactile) perception, in accordance with embodiments of the present disclosure. According to some embodiments, method  500  may begin at step  502 . As noted above, teachings of the present disclosure may be implemented in a variety of configurations of test system  400 . As such, the preferred initialization point for method  500  and the order of the steps comprising method  500  may depend on the implementation chosen. 
     At step  502 , test module  408  executing on processor  402  may apply a haptic playback waveform a(t) selected from candidate waveforms  410  to the input of amplifier  406 , which in turn may amplify haptic playback waveform a(t) to generate an amplified haptic playback waveform a′(t) (e.g., a voltage signal) at the input of linear resonant actuator  107 .  FIG. 6A  illustrates an example haptic playback waveform a(t), in accordance with embodiments of the present disclosure. 
     In response, at step  504 , linear resonant actuator  107  may vibrate as a function of amplified haptic playback waveform a′(t), and acceleration generated by linear resonant actuator  107  may be measured by accelerometer  412 , which may generate an acceleration response signal x(t) indicative of such measured acceleration.  FIG. 6B  illustrates an example acceleration response signal x(t) measured in response to the example haptic playback waveform a(t) shown in  FIG. 6A , in accordance with embodiments of the present disclosure. In  FIG. 6B , example acceleration response signal x(t) is depicted in units of acceleration (e.g., in terms of the net acceleration that is imparted to objects due to the combined effect of gravitation from distribution of mass within Earth and the centrifugal force from the Earth&#39;s rotation, which is denoted as “g”). 
     At step  506 , processor  402  may receive acceleration response signal x(t) and test module  408  may read acceleration response signal x(t) and partition it into two parts: a main pulse x m (t) and a resonant tail x r (t), as shown in  FIG. 6B . For example, main pulse x m (t) may represent the portion of acceleration response signal x(t) from time zero until acceleration response signal x(t) has decayed to a certain percentage (e.g., 10 percent) of its peak value, while resonant tail x r (t) may represent the remainder of acceleration response signal x(t). 
     At step  508 , test module  408  may obtain a perceptual haptic sensitivity model H(f) that is proportional to the inverse of a haptic perceptual threshold curve U(f) (e.g., H(f)∝1/U(f)).  FIG. 7  depicts an example of a haptic perceptual threshold curve U(f), in accordance with embodiments of the present disclosure. In research performed in the scientific areas of neural physiology and vibro-tactile perception, mechanoreceptors in skin of a human may sense mechanical vibration and transmit signals to the brain of the human to form haptic perceptions. One of such mechanoreceptors, the Pacinian corpuscles, is sensitive to such vibrations applied to skin of a human finger. The sensitive region of Pacinian corpuscles is above 40 Hz, with peak sensitivity around 200 Hz to 300 Hz. The sensitivity of the Pacinian neuro-receptors may be characterized by a U-shaped threshold curve U(f) (an example of which is shown in  FIG. 7 ), with its minimum around 150 Hz to 250 Hz, which frequency region corresponds to maximum haptic sensitivity of human finger skin. 
     At step  510 , test module  408  may apply perceptual haptic sensitivity model H(f) (e.g., in order to perform haptic perceptual filtering) to main pulse x m (t), in either the time domain or the frequency domain, to obtain a haptic-perceptible component x m   h (t) of main pulse x m (t). If in the time domain, such application of perceptual haptic sensitivity model H(f) may correspond to convolutive filtering as:
 
 x   m   h ( t )= x   m ( t )* h ( t ),
 
where h(t)=F −1 {H(f)} is the inverse Fourier transform of the haptic sensitivity model. If in the frequency domain, such application of perceptual haptic sensitivity model H(f) may be given as:
 
 x   m   h ( f )= X   m ( f )· H ( f ),
 
where X(t)=F{x m (t)} is the Fourier transform of the main-pulse signal x m (t).
 
     At step  512 , in a similar manner to that of step  510 , test module  408  may apply perceptual haptic sensitivity model H(f) to resonant tail x r (t), in either the time domain or the frequency domain, to obtain a haptic-perceptible component x r   h (t) of resonant tail x r (t). If in the time domain, such application of perceptual haptic sensitivity model H(f) may be given as:
 
 x   r   h ( t )= x   r ( t )* h ( t )
 
If in the frequency domain, such application of perceptual haptic sensitivity model H(f) may be given as:
 
 X   r   h ( f )= X   r ( f )· H ( f )
 
     At step  514 , test module  408  may calculate a perceptual haptic-sharpness score as a perceptual pulse-to-resonance ratio or perceptual pulse-to-ringing ratio (PPRR) value from the above-obtained haptic-perceptible components of main pulse signal x m (t) and resonant tail signal x r (t), x m   h (t) and x r   h (t). The PPRR value in dB, dbPPRR, may be defined as the ratio of the perceptual energy of main pulse to that of the resonant tail: 
     
       
         
           
             
               S 
               h 
             
             = 
             
               dbPPRR 
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                 20 
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                     log 
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                       RMS 
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                             ( 
                             t 
                             ) 
                           
                         
                         ) 
                       
                     
                     
                       
                         RMS 
                         ⁡ 
                         
                           ( 
                           
                             
                               x 
                               r 
                               h 
                             
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                               t 
                               ) 
                             
                           
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                       ⁢ 
                       
                           
                       
                     
                   
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     In some embodiments, at step  516 , test module  408  may revise the perceptual haptic-sharpness score calculated in step  514  above for emphasis on a subjective feeling of “crispness” and obtain a perceptual haptic-crispness score (PHCS), by weighting dbPPRR with a crispness factor C:
 
 s   h   =C·db PPRR
 
An example of such a crispness factor C may be a crest factor of the main pulse signal x m (t):
 
 C =CrestFactor{ x   m ( t )},
 
wherein, the crest factor of x m (t) may be defined as its peak-to-RMS ratio:
 
               CrestFactor   ⁢     {       x   m     ⁡     (   t   )       }       =       Max   ⁢     {            x   m     ⁡     (   t   )            }         RMS   ⁢     {       x   m     ⁡     (   t   )       }               
Another example of a crispness factor C may be given by:
 
             C   =     α       Time   ⁢           ⁢   duration   ⁢           ⁢     {       x   m     ⁡     (   t   )       }       +   β             
where α and β are constants.
 
     While specific examples for calculation of crispness factor C are given above, there may be other forms of definition for crispness factor C, wherein such crispness factor C take into account a duration of main pulse signal x m (t) and a rate of change in main pulse signal x m (t) to provide an indication of subjective crispness of a haptic response. 
     The proposed perceptual sharpness score (S h =dbPPRR) and the optional perceptual crispness score (S h =C·dbPPRR) may thus provide a quantification of haptic signal fidelity, with more perceptual-relevant objective measures for subjective haptic sharpness and crispness evaluations of the virtual mechanical button responses generated by linear resonant actuator  107 , as compared to existing approaches to measuring haptic responses. 
     Although  FIG. 5  discloses a particular number of steps to be taken with respect to method  500 , method  500  may be executed with greater or fewer steps than those depicted in  FIG. 5 . In addition, although  FIG. 5  discloses a certain order of steps to be taken with respect to method  500 , the steps comprising method  500  may be completed in any suitable order. 
     Method  500  may be implemented in whole or part using processor  402 , test module  408 , and/or any other system operable to implement method  500 . In certain embodiments, method  500  may be implemented partially or fully in software and/or firmware embodied in computer-readable media. 
       FIG. 8  illustrates a flow chart of an example method  800  for automatic evaluation and design of haptic stimuli, in accordance with embodiments of the present disclosure. According to some embodiments, method  800  may begin at step  802 . As noted above, teachings of the present disclosure may be implemented in a variety of configurations of test system  400 . As such, the preferred initialization point for method  800  and the order of the steps comprising method  800  may depend on the implementation chosen. 
     At step  802 , test module  408  may apply a haptic playback waveform a(t) selected from candidate waveforms  410  to the input of amplifier  406 , which in turn may amplify haptic playback waveform a(t) to generate an amplified haptic playback waveform a′(t) (e.g., a voltage signal) at the input of linear resonant actuator  107 . 
     At step  804 , linear resonant actuator  107  may vibrate as a function of amplified haptic playback waveform a′(t), and acceleration generated by linear resonant actuator  107  may be measured by accelerometer  412 , which may generate an acceleration response signal x(t) indicative of such measured acceleration. 
     At step  806 , processor  402  may receive acceleration response signal x(t) and test module  408  may analyze acceleration response signal x(t) and characterize acceleration response signal x(t) in order to place acceleration response signal x(t) in a perceptual haptic sharpness/intensity diagram. To illustrate, in the design of actual haptic-system and haptic-stimulus waveforms, it may be desirable to generate sharp haptic perception, and it may be desirable that the perceived intensity of the haptic responses is strong. In addition, with different combinations of sharpness and intensity levels, various haptic effects may be achieved, and each one may focus on different application scenarios. Therefore, in accordance with embodiments of the present disclosure, a perceptual sharpness-intensity diagram (PSID) may be used to differentiate such variations and differences, as well as to evaluate the performance of various haptic stimulus waveforms and haptic clicking devices. Based on the perceptual sharpness-intensity diagram disclosed herein, more efficient and perceptual-relevant automatic evaluations of haptic click designs may be achieved. In addition, procedures for potential automatic haptic playback waveform designs may also be defined. 
       FIG. 9  illustrates an example of a haptic sharpness diagram, in accordance with embodiments of the present disclosure. A perceptual haptic sharpness/intensity diagram (PHSID) may be a two-dimensional plot that displays a joint distribution (S h,  I h ) of the above-mentioned perceptual sharpness score S h  and a perceptual haptic intensity (PHI) level (I h ) of haptic vibrations generated by linear resonant actuator  107 . The calculation of PHI level I h , may also be based on the perceptual haptic sensitivity model described above. For example, as described above in relation to step  510  of method  500 , a perceptual main pulse signal x m   h (t) may be obtained from the vibrational measurement. Perceptual haptic intensity I h  may be defined as a strength of perceptual main pulse signal x m   h (t), and depending on different strength definitions, there may be several definitions for the perceptual haptic intensity level. For example, in some embodiments, perceptual haptic intensity I h  of perceptual main pulse signal x m   h (t) may be given as the root-mean-square level of perceptual main pulse signal x m   h (t):
 
 I   h =RMS{ x   m   h ( t )}
 
As another example, in other embodiments, perceptual haptic intensity I h  of perceptual main pulse signal x m   h (t) may be given as the peak level of perceptual main pulse signal x m   h (t):
 
 I   h =Max{| x   m   h ( t )|}
 
     When both the perceptual sharpness score S h  and the perceptual haptic intensity I h  are available, a location of the (S h , I h ) pair gives, in a perceptual haptic sharpness/intensity diagram, such as that shown in  FIG. 9 , a position of a haptic system under test in terms of haptic performances in both sharpness and intensity together. Such perceptual haptic sharpness and intensity diagram may be used to evaluate and compare vibro-haptic performances of different linear resonant actuator devices and/or evaluate and compare haptic performances of different haptic playback waveforms designed and played through a linear resonant actuator. To that end,  FIG. 9  provides an example of haptic sharpness/intensity distributions of multiple haptic playback waveforms (shown as points in  FIG. 9 ), measured from a single linear resonant actuator driven by such haptic playback waveforms. 
     Turning back to  FIG. 8 , at step  808 , test module  408  may sort test results in terms of perceptual sharpness score or, optionally, perceptual crispiness score, each measurement (S h , I h ) in the perceptual haptic sharpness/intensity diagram, and compare with minimum requirement thresholds for S h  and I h  for acceptable designs. At step  810 , if either a perceptual sharpness/crispiness score S h  is below a required threshold, or a perceptual haptic intensity level I h  is too low, method  800  may proceed to step  812 . Otherwise, method  800  may proceed to step  814 . 
     At step  812 , test module  408  may generate a varied design of a haptic playback waveform and then method  800  may proceed again to step  804 . 
     At step  814 , test module  408  may end the design and evaluation procedure and store (e.g., in memory  204 ) the best haptic playback waveforms obtained (e.g., those having the highest perceptual sharpness/crispiness score S h  values and acceptable intensity levels of perceptual haptic intensity level I h ). After completion of step  814 , method  800  may end. 
     Although  FIG. 8  discloses a particular number of steps to be taken with respect to method  800 , method  800  may be executed with greater or fewer steps than those depicted in  FIG. 8 . In addition, although  FIG. 8  discloses a certain order of steps to be taken with respect to method  800 , the steps comprising method  800  may be completed in any suitable order. 
     Method  800  may be implemented in whole or part using processor  402 , test module  408 , and/or any other system operable to implement method  800 . In certain embodiments, method  800  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.