Inductive three-axis lens position measurement using AF and OIS coils
Some embodiments include a camera of a mobile computing device. In some embodiments, the camera includes an autofocus coil for moving a lens module, a plurality of optical image stabilization coils, a driver circuit element, connected to the autofocus coil, for passing an alternating current waveform through the autofocus coil, and one or more measurement circuit elements, connected to respective ones of the plurality of the optical image stabilization coils, for measuring changes induced in currents in the respective ones of the plurality of the optical image stabilization coils by the waveform.
1. A camera of a mobile computing device, comprising:
a lens module;
an image sensor;
an autofocus coil and one or more optical image stabilization coils configured to generate relative motion between the image sensor and the lens module, wherein
the autofocus coil is mechanically connected to one or more of the lens module and the image sensor, and
each of the one or more optical image stabilization coils is mechanically connected to one or more of the lens module and the image sensor;
one or more driver circuit elements, connected to the autofocus coil, configured to pass a current through the autofocus coil; and
one or more measurement circuit elements connected to respective ones of the one or more optical image stabilization coils, the one or more measurement circuit elements configured to measure changes induced in currents in the respective ones of the one or more optical image stabilization coils to enable determination of a position of the autofocus coil.
2. The camera of claim 1 , wherein
the one or more driver circuit elements comprise an AC driver circuit element, connected to the autofocus coil, for passing an alternating current waveform through the autofocus coil; and
the one or more measurement circuits comprise one or more AC measurement circuit elements, connected to respective ones of the one or more optical image stabilization coils, for measuring changes induced in currents in the respective ones of the one or more optical image stabilization coils by the alternating current waveform.
3. The camera of claim 1 , wherein
the autofocus coil comprises a coil for generating force to compel relative motion between the image sensor and the lens module along an optical axis between the image sensor and a lens of the lens module; and
the one or more optical image stabilization coils comprise one or more of optical image stabilization coils for generating force to compel relative motion between the image sensor and the lens module along one or more directions orthogonal to the optical axis between the image sensor and a lens of the lens module.
4. The camera of claim 1 , wherein the one or more measurement circuit elements further comprise:
one or more voltage measurement elements for measuring voltage differences created by the changes induced in the currents in the respective ones of the one or more optical image stabilization coils by an alternating current waveform.
5. The camera of claim 1 , wherein
the one or more measurement circuit elements further comprise measurement elements capable of detecting components of motion of the autofocus coil in at least a direction of an optical axis of the lens module and at least two directions perpendicular to the optical axis.
6. The camera of claim 1 , wherein
the one or more measurement circuit elements further comprise measurement elements capable of detecting components of motion of the autofocus coil in at least a direction of an optical axis of the lens module and at least two directions perpendicular to the optical axis; and
the camera excludes dedicated magnetic field sensors for detecting motion of the autofocus coil.
7. The camera of claim 1 , wherein
the one or more measurement circuit elements further comprise measurement elements capable of detecting components of motion of the autofocus coil in at least a direction of an optical axis of the lens module and at least two directions perpendicular to the optical axis; and
the camera excludes dedicated capacitance sensors for detecting motion of the autofocus coil.
8. The camera of claim 1 , wherein
the one or more measurement circuit elements further comprise measurement elements capable of detecting components of motion of the autofocus coil in at least a direction of an optical axis of the lens module and at least two directions perpendicular to the optical axis; and
the camera excludes dedicated optical range finder sensors for detecting motion of the autofocus coil.
9. A method for measuring a position of an autofocus coil, comprising:
delivering an alternating electrical signal to the autofocus coil that is distinct from one or more optical image stabilization coils; and
calculating a position of the autofocus coil by measuring a voltage associated with a current induced in one or more of the optical image stabilization coils by the alternating current delivered to the autofocus coil.
10. The method of claim 9 , wherein
calculating a position of the autofocus coil further comprises:
generating closed loop feedback measurement of a position of a lens module associated with the autofocus coil with respect to three or more axes.
11. The method of claim 9 , wherein
the measuring the voltage associated with the current induced in the one or more optical image stabilization coils by the alternating current further comprises:
measuring the voltage when an image sensor associated with the autofocus coil is not performing an exposure to reduce image capture noise associated with the image sensor being active.
12. The method of claim 9 , wherein
the delivering the alternating electrical signal to the autofocus coil further comprises:
delivering a zero-mean current waveform applied in superposition to the existing drive current of an actuator used to move a lens module of a digital camera; and
measuring the voltage associated with the current induced in the one or more optical image stabilization coils by the alternating current.
13. The method of claim 9 , wherein
the delivering the alternating electrical signal to the autofocus coil further comprises:
delivering the alternating electrical signal to the autofocus coil through a PWM type AF coil drive scheme.
14. The method of claim 9 , wherein
the delivering the alternating electrical signal to the autofocus coil further comprises:
adjusting a position of a lens module using a closed-loop feedback based upon the measuring.
15. A camera actuator, comprising:
an autofocus coil for moving a lens module;
a plurality of optical image stabilization coils that are distinct from the autofocus coil;
a driver circuit element, connected to the autofocus coil, for passing an alternating current waveform through the autofocus coil; and
one or more measurement circuit elements, connected to respective ones of the plurality of the optical image stabilization coils, for measuring changes induced in currents in the respective ones of the plurality of the optical image stabilization coils by the waveform passing through the autofocus coil.
16. The camera actuator of claim 15 , wherein the one or more measurement circuit elements further comprise:
one or more voltage measurement elements for measuring voltage differences created by the changes induced in the currents in the respective ones of the plurality of the optical image stabilization coils by the waveform.
17. The camera actuator of claim 15 , wherein
the one or more measurement circuit elements further comprise measurement elements capable of detecting components of motion of the autofocus coil in at least a direction of an optical axis of the lens module and at least two directions perpendicular to the optical axis.
18. The camera actuator of claim 15 , wherein
the one or more measurement circuit elements further comprise measurement elements capable of detecting components of motion of the autofocus coil in at least a direction of an optical axis of the lens module and at least two directions perpendicular to the optical axis; and
the camera excludes dedicated magnetic field sensors for detecting motion of the autofocus coil.
19. The camera actuator of claim 15 , wherein
the one or more measurement circuit elements further comprise measurement elements capable of detecting components of motion of the autofocus coil in at least a direction of an optical axis of the lens module and at least two directions perpendicular to the optical axis; and
the camera excludes dedicated capacitance sensors for detecting motion of the autofocus coil.
20. The camera actuator of claim 15 , wherein
the autofocus coil comprises a coil for generating force to compel relative motion between the lens module and an image sensor along an optical axis between a lens of the lens module and the image sensor; and
the plurality of optical image stabilization coils comprise coils for generating force to compel relative motion between the lens module and the image sensor along one or more directions orthogonal to the optical axis between the lens of the lens module and the image sensor.