Vibrational transducer control
A method of controlling a vibrational transducer, the method comprising: tracking a temperature metric of the vibrational transducer; and controlling a drive signal for the vibrational transducer, where the drive signal is limited to a value to protect the vibrational transducer from over excursion, and where said value is a function of the tracked temperature metric.
1. A method of controlling a vibrational transducer, the method comprising:
tracking a temperature metric of the vibrational transducer; and
controlling a drive signal for the vibrational transducer, where the drive signal is limited to a value to protect the vibrational transducer from over excursion, and where said value is a function of the tracked temperature metric;
wherein the method comprises:
generating the drive signal based on an input signal; and
generating said temperature metric based on an excursion difference, being a difference between a predicted excursion, predicted by an excursion prediction model based on the input signal or the drive signal, and a direct displacement value, generated based upon a current drawn by the vibrational transducer and/or a voltage across the vibrational transducer.
2. The method according to claim 1 , comprising adjusting said value based on the temperature metric to reduce, or at least partly compensate for an effect of, the temperature of the vibrational transducer on:
the over-excursion protection; and/or
mechanical clipping of the vibrational transducer; and/or
a probability or risk of mechanical clipping of the vibrational transducer; and/or
a rate of incidence of mechanical clipping of the vibrational transducer.
3. The method according to claim 1 , wherein:
said temperature metric is indicative of a temperature of the vibrational transducer; and/or
said temperature metric is a measure of the temperature of the overall vibrational transducer; and/or
the vibrational transducer comprises a plurality of sub-components including a coil, and said temperature metric is a measure of the temperature, or a representative temperature, of a combination of the plurality of sub-components.
4. The method according to claim 3 , wherein the plurality of sub-components comprises the coil, an enclosure, a moveable mass, and a spring.
5. The method according to claim 1 , comprising generating said temperature metric based on one or more signals and/or electrical properties of the vibrational transducer.
6. The method according to claim 1 , comprising generating said temperature metric by at least one of:
obtaining a reading from a thermal sensor of, or proximal to, the vibrational transducer;
measuring an impedance of a coil of the vibrational transducer, and estimating a temperature of the coil based on the measured impedance;
using a thermal model to track a temperature change of the coil based on input power to the vibrational transducer; and
using a thermal model to track a temperature change of the overall vibrational transducer based on the input power to the vibrational transducer.
7. The method according to claim 1 , comprising:
limiting a voltage or current of the drive signal to protect the vibrational transducer from over excursion;
retrieving a voltage limit value or a current limit value from a memory based on the tracked temperature metric; and/or
controlling the drive signal by adapting a control model or a predictive model based on the tracked temperature metric; and/or
estimating whether excursion of the vibrational transducer is close to over excursion and/or a clipping condition based on the temperature metric, and setting said value based on the estimation, optionally wherein the value is derived from an excursion model adapted using the temperature metric; and/or
defining or storing, optionally in a look-up table, a set of said values, being limit values, corresponding respectively to different values or ranges of values of the temperature metric, and selecting a limit value based on the correspondence between said limit values and values of the temperature metric.
8. The method according to claim 1 , comprising:
using an excursion prediction model to predict an excursion of the vibrational transducer based on the input signal;
generating the drive signal based on the predicted excursion, or on the input signal and the predicted excursion; and
adjusting the excursion prediction model based on the temperature metric to adjust said value.
9. The method according to claim 8 , wherein the adjusting the excursion prediction model comprises at least one of:
adjusting one or more parameters of the excursion prediction model; and
selecting the excursion prediction model from a plurality of candidate excursion prediction models.
10. The method according to claim 1 , comprising:
using a direct displacement model to generate a direct displacement value, being a measure of the excursion of the vibrational transducer, based upon a current drawn by the vibrational transducer and/or a voltage across the vibrational transducer;
generating the drive signal based on the direct displacement value, or on the input signal and the direct displacement value; and
adjusting the direct displacement model based on the temperature metric to adjust said value.
11. The method according to claim 10 , wherein the adjusting the direct displacement model comprises at least one of:
adjusting one or more parameters of the direct displacement model; and
selecting the direct displacement model from a plurality of candidate direct displacement models.
12. The method according to claim 1 , comprising:
calculating an excursion difference, being a difference between a predicted excursion, predicted by an excursion prediction model based on the input signal, and a direct displacement value, being a measure of the excursion of the vibrational transducer, generated by a direct displacement model based upon a current drawn by the vibrational transducer and/or a voltage across the vibrational transducer;
generating the drive signal based on the excursion difference, or on the input signal and the excursion difference; and
adjusting the excursion prediction model and/or the direct displacement model based on the temperature metric to adjust said value.
13. The method according to claim 12 , wherein the adjusting the excursion prediction model and/or the direct displacement model comprises at least one of:
adjusting one or more parameters of the excursion prediction model and/or the direct displacement model; and
selecting the excursion prediction model and/or the direct displacement model from a plurality of candidate models.
14. The method according to claim 1 , comprising controlling a relationship between the drive signal and the input signal based on the temperature metric to adjust said value.
15. A controller for controlling a vibrational transducer, the controller configured to carry out the method of claim 1 .
16. A host device, being an electrical or electronic device, comprising the controller according to claim 15 .