Detection and prevention of non-linear excursion in a haptic actuator
A method for determining and mitigating over-excursion of an internal mass of an electromechanical transducer may include measuring a sensed signal associated with the electromechanical transducer in response to a driving signal driven to the electromechanical transducer, determining a non-linearity value based on the sensed signal, mapping the non-linearity value to a probability of over-excursion of the internal mass, and applying a gain to a signal path configured to generate the driving signal based on the probability.
1. A method for determining and mitigating over-excursion of an internal mass of an electromechanical transducer, the method comprising:
measuring a sensed signal associated with the electromechanical transducer in response to a driving signal driven to the electromechanical transducer;
determining a non-linearity value based on the sensed signal;
mapping the non-linearity value to a probability of over-excursion of the internal mass; and
applying a gain to a signal path configured to generate the driving signal based on the probability.
2. The method of claim 1 , wherein determining the non-linearity value based on the sensed signal comprises determining a back-electromotive force associated with the electromechanical transducer based on the sensed signal.
3. The method of claim 1 , wherein determining the non-linearity value comprises:
determining a first content ratio equal to a ratio of content present in the driving signal in a first frequency band to content present in the driving signal in a second frequency band;
determining a second content ratio equal to a ratio of content present in the sensed signal in the first frequency band to content present in the second frequency band; and
determining the non-linearity value based on a comparison of the first content ratio and the second content ratio.
4. The method of claim 1 , wherein determining the non-linearity value comprises:
determining a first content ratio equal to a ratio of high-frequency content present in the driving signal above a particular frequency to low-frequency content present in the driving signal below the particular frequency;
determining a second content ratio equal to a ratio of high-frequency content present in the sensed signal above the particular frequency to low-frequency content present in the sensed signal below the particular frequency; and
determining the non-linearity value based on a comparison of the first content ratio and the second content ratio.
5. The method of claim 1 , wherein determining the non-linearity value comprises determining the non-linearity value based on noise gating of a magnitude of the driving signal compared to noise gating of a magnitude of the sensed signal.
6. The method of claim 1 , wherein determining the non-linearity value comprises:
generating the driving signal as a pilot tone at a frequency greater than a resonance frequency of electromechanical transducer;
measuring total harmonic distortion present in the sensed signal in response to the pilot tone; and
determining the non-linearity value based on the total harmonic distortion.
7. The method of claim 1 , further comprising attenuating the driving signal based on the gain.
8. The method of claim 1 , wherein:
determining the non-linearity value based on the sensed signal comprises measuring harmonic components of the sensed signal; and
the method further comprises determining an orientation of the electromagnetic transducer based on amplitude and phase of harmonic components of the sensed signal.
9. The method of claim 1 , wherein:
the driving signal is a voltage signal; and
the sensed signal is a current signal.
10. The method of claim 1 , wherein the electromagnetic transducer is one of a haptic transducer, a voice coil, and a loudspeaker.
11. A system for determining and mitigating over-excursion of an internal mass of an electromechanical transducer, the system comprising:
an input configured to measure a sensed signal associated with the electromechanical transducer in response to a driving signal driven to the electromechanical transducer; and
a non-linear excursion detector configured to:
determine a non-linearity value based on the sensed signal;
map the non-linearity value to a probability of over-excursion of the internal mass; and
apply a gain to a signal path configured to generate the driving signal based on the probability.
12. The system of claim 11 , wherein determining the non-linearity value based on the sensed signal comprises determining a back-electromotive force associated with the electromechanical transducer based on the sensed signal.
13. The system of claim 11 , wherein determining the non-linearity value comprises:
determining a first content ratio equal to a ratio of content present in the driving signal in a first frequency band to content present in the driving signal in a second frequency band;
determining a second content ratio equal to a ratio of content present in the sensed signal in the first frequency band to content present in the second frequency band; and
determining the non-linearity value based on a comparison of the first content ratio and the second content ratio.
14. The system of claim 11 , wherein determining the non-linearity value comprises:
determining a first content ratio equal to a ratio of high-frequency content present in the driving signal above a particular frequency to low-frequency content present in the driving signal below the particular frequency;
determining a second content ratio equal to a ratio of high-frequency content present in the sensed signal above the particular frequency to low-frequency content present in the sensed signal below the particular frequency; and
determining the non-linearity value based on a comparison of the first content ratio and the second content ratio.
15. The system of claim 11 , wherein determining the non-linearity value comprises determining the non-linearity value based on noise gating of a magnitude of the driving signal compared to noise gating of a magnitude of the sensed signal.
16. The system of claim 11 , wherein determining the non-linearity value comprises:
generating the driving signal as a pilot tone at a frequency greater than a resonance frequency of electromechanical transducer;
measuring total harmonic distortion present in the sensed signal in response to the pilot tone; and
determining the non-linearity value based on the total harmonic distortion.
17. The system of claim 11 , wherein the non-linear excursion detector is further configured to attenuate the driving signal based on the gain.
18. The system of claim 11 , wherein:
determining the non-linearity value based on the sensed signal comprises measuring harmonic components of the sensed signal; and
the method further comprises determining an orientation of the electromagnetic transducer based on amplitude and phase of harmonic components of the sensed signal.
19. The system of claim 11 , wherein:
the driving signal is a voltage signal; and
the sensed signal is a current signal.
20. The system of claim 11 , wherein the electromagnetic transducer is one of a haptic transducer, a voice coil, and a loudspeaker.