Method and device for position sensing of an optical component in an imaging system

1. An imaging system comprising:

an image sensor located at an image plane;

at least a lens element for projecting an image on the image sensor, the lens element defining an optical axis;

a driving mechanism, operatively connected to the lens element, for shifting the lens element relative to the image sensor in a direction substantially parallel to the optical axis;

a light source for providing a light beam to illuminate a spot on a surface of the lens element so as to produce a reflected light beam from the spot on said surface, wherein the light source is so positioned that the reflected light beam is arranged to encounter the image sensor at a location on the image sensor; and

a processor, operatively connected to the image sensor, for determining the encountering location, wherein when the lens element is shifted by a shifting distance, said encountering location is moved within the image sensor by a moving distance, the processor is configured to compute the shifting distance of the lens element based on the moving distance of the encountering location.

2. The imaging system of claim 1 , wherein the light source comprises a laser.

3. The imaging system of claim 1 , wherein the light source comprises an light emitting element.

4. The imaging system of claim 1 , wherein the processor is configured to capture image frames from the image sensor and to determine the encountered location based on data transferred from the image sensor between image frames, and wherein the light source comprises a pulsed light source in synchronism to the frame capture such that the reflected light beam is arranged to encounter the image sensor at a location on the image sensor also between image frames.

5. The imaging system of claim 4 , wherein amount of the data transferred for determining the encountered location is smaller than amount of data transferred for frame capture.

6. The imaging system of claim 1 , further comprising a control module, operatively connected to the driving mechanism for adjusting the lens element based on the computed shifting distance.

7. The imaging system of claim 6 , further comprising a memory module for storing calibration data for said adjusting.

8. A method for position sensing, comprising:

providing a light beam in relationship to a lens element in an imaging system to illuminate a spot on a surface of the lens element so as to produce a reflected light beam from the spot on said surface, wherein the imaging system comprises an image sensor and the lens element is arranged to project an image on the image sensor along an optical axis, and the lens element is shiftable relative to the image sensor in a direction substantially parallel to the optical axis, and wherein the light beam is so positioned that the reflected light beam encounters the image sensor at a location on the image sensor, and wherein when the lens element is shifted by a shifting distance, said encountering location is moved within the image sensor by a moving distance; and

determining the moving distance of said encountering location for computing the shifting distance of the lens element based on the moving distance of the encountering location.

9. The method of claim 8 , further comprising:

adjusting position of the lens element based on the computed shifting distance.

10. The method of claim 9 , further comprising:

adjusting the computed shifting distance based on calibration data.

11. A position sensing module for use in an imaging system, comprising:

a light source for providing a light beam to illuminate a spot on a surface of a lens element of the imaging system so as to produce a reflected light beam from the spot on said surface, wherein the imaging system comprises an image sensor at an image plane and the lens element is arranged to project an image on the image sensor along an optical axis, and the lens element is shiftable relative to the image sensor in a direction substantially parallel to the optical axis, and wherein the light source is so positioned that the reflected light beam is arranged to encounter the image sensor at a location on the image sensor; and

a processor, operatively connected to the image sensor, for determining the encountering location, wherein when the lens element is shifted by a shifting distance, said encountering location is moved within the image sensor by a moving distance, the processor is configured to compute the shifting distance of the lens element based on the moving distance of the encountering location.

12. The position module of claim 11 , further comprising a memory module for storing calibration data for adjusting the computed shifting distance based on the calibration data.

13. An imaging system, comprising:

means for projecting an image along an optical axis, said projecting means including a lens element having a lens surface;

means for sensing the image at an image plane;

means for shifting the lens element relative to the image sensor in a direction substantially parallel to the optical axis;

means for illuminating a spot on the lens surface so as to produce a reflected light beam from the spot on said surface such that the reflected light beam encounters the image sensing means at a location on the image sensing means; and

means, configured to read out information from the image sensing means, for determining the encountering location, wherein when the lens element is shifted by a shifting distance, said encountering location is moved within the image sensing means by a moving distance, the determining means is configured to compute the shifting distance of the lens element based on the moving distance of the encountering location.

14. The imaging system of claim 13 , further comprising:

means for adjusting position of the lens element based on the computed shifting distance.

15. The imaging system of claim 14 , further comprising:

means for storing calibration data, wherein the position adjusting is based on the calibration data.