Active lens alignment system
For aligning an image sensor relative to a lens module prior to fixing the image sensor to the lens module, an exposure of the image sensor is turned on and the image sensor is moved to different distances relative to the lens module. At certain predetermined distances between the image sensor and the lens module, a calibration pattern is illuminated and two or more pictures of the calibration pattern which is focused through the lens module are captured with the image sensor to produce at least two pictures of the calibration pattern captured at different distances, the at least two pictures being superimposed onto a calibration image. The exposure of the image sensor is then turned off and the pictures of the calibration pattern are analyzed for determining an alignment between the lens module and the image sensor.
1. A method for aligning an image sensor relative to a lens module prior to fixing the image sensor to the lens module, the method comprising the steps of:
turning on an exposure of the image sensor and moving the image sensor to different distances relative to the lens module;
at certain predetermined distances between the image sensor and the lens module, illuminating a calibration pattern and capturing with the image sensor two or more pictures of the calibration pattern which is focused through the lens module to produce at least two pictures of the calibration pattern captured at different distances, the at least two pictures being superimposed onto a calibration image;
turning off the exposure of the image sensor; and
analyzing the pictures of the calibration pattern that are superimposed onto the calibration image for determining an alignment between the lens module and the image sensor.
2. The method as claimed in claim 1 , further comprising the step of holding the lens module with a gripper assembly and adjusting the lens module with the gripper assembly to achieve the alignment that has been determined prior to fixing the image sensor to the lens module.
3. The method as claimed in claim 1 , wherein the calibration pattern is contained in a collimator module which is operative to direct the chart pattern to the image sensor through the lens module.
4. The method as claimed in claim 3 , wherein the collimator module further comprises a plurality of collimators that are distributed such that each collimator is operative to direct a separate calibration pattern onto a different area of the calibration image.
5. The method as claimed in claim 4 , wherein the different areas of the calibration image comprise regions corresponding to at least four corners of the calibration image.
6. The method as claimed in claim 4 , wherein the collimators are positioned equidistant to one another.
7. The method as claimed in claim 4 , wherein the collimators comprise a central collimator positioned vertically and a plurality of inclined collimators that surround the central collimator, and each inclined collimator is tilted at an oblique angle with respect to the central collimator.
8. The method as claimed in claim 4 , wherein each collimator comprises a calibration pattern, a light source for illuminating the calibration pattern and a lens assembly for directing the illuminated calibration pattern towards the image sensor.
9. The method as claimed in claim 8 , wherein the calibration pattern contains a chart including a slanted edge pattern appearing on it.
10. The method as claimed in claim 1 , wherein the step of moving the image sensor to different distances relative to the lens module further comprises the step of moving a positioning table on which the image sensor is supported for positioning the image sensor.
11. The method as claimed in claim 1 , wherein the step of moving the image sensor further comprises the step of simultaneously moving the image sensor to varying vertical positions as well as varying horizontal positions relative to the lens module.
12. The method as claimed in claim 11 , wherein the step of illuminating the calibration pattern is conducted at predetermined vertical positions of the image sensor relative to the lens module.
13. The method as claimed in claim 12 , wherein the different vertical positions of the image sensor are actuated by a stepper motor such that a motor count of the stepper motor represents a current height of the image sensor.
14. The method as claimed in claim 1 , wherein the step of determining the said alignment further comprises the step of comparing respective points of focus of the calibration patterns captured at different distances for the best focusing distance of the image sensor relative to the lens module.
15. The method as claimed in claim 14 , wherein the best focusing distance is determined from the distance at which an edge transition width of a superimposed calibration pattern is the best.
16. The method as claimed in claim 1 , wherein each picture of the calibration pattern that is superimposed onto the calibration image captured by the image sensor is shifted with respect to another picture of the calibration pattern on the calibration image.