Lens assembly with integrated feedback loop for focus adjustment

Patent metadata

Field	Value
Publication number	US-11513311-B2
Application number	US-202016927732-A
Country	US
Kind code	B2
Filing date	Jul 13, 2020
Priority date	Mar 13, 2013
Publication date	Nov 29, 2022
Grant date	Nov 29, 2022

Abstract

This invention provides a removably mountable lens assembly for a vision system camera that includes an integral auto-focusing liquid lens unit, in which the lens unit compensates for focus variations by employing a feedback control circuit that is integrated into the body of the lens assembly. The feedback control circuit receives motion information related to the bobbin of the lens from a position sensor (e.g. a Hall sensor) and uses this information internally to correct for motion variations that deviate from the lens setting position at a desired lens focal distance setting. Illustratively, the feedback circuit can be interconnected with one or more temperature sensors that adjust the lens setting position for a particular temperature value. In addition, the feedback circuit can communicate with an accelerometer that reads a direction of gravity and thereby corrects for potential sag in the lens membrane based upon the spatial orientation of the lens.

First claim

What is claimed is:

1. A method for controlling focus of a membrane-based liquid lens assembly of a vision system camera comprising the steps of:
reading, with a local controller mounted in a lens body containing the liquid lens assembly, a target focal position received from a vision system processor of a vision system camera and determining, based on the target focal position, a target position of an actuator of the membrane-based liquid lens assembly;
measuring, based upon a position sensor associated with movement of the actuator, an actual position of the actuator;
comparing the measured actual position with the target position, and determining a corrected position that is associated with the target position; and
instructing movement of a position of the actuator to the corrected position.

2. The method as set forth in claim 1 further comprising signaling when the actuator has successfully moved to the corrected position.

3. The method as set forth in claim 1 , further comprising, correcting the target position based upon at least one of (a) a measured temperature of the liquid lens assembly, (b) a spatial orientation of the liquid lens assembly relative to an acting direction of gravity and (c) a stored sensor-to-flange distance tolerance associated with a mount of the lens body.

4. The method as set forth in claim 1 wherein the step of measuring the actual position comprises receiving a measurement value from at least one Hall sensor.

5. The method as set forth in claim 1 wherein the step of instructing movement comprises varying current to a bobbin based upon a controller.

6. The method as set forth in claim 1 wherein the step of determining the target position comprises determining a position that focuses an image acquired by the vision system camera.

7. The method as set forth in claim 6 wherein the target position defines position information that is further corrected for at least one of temperature of the liquid lens assembly, spatial orientation of the liquid lens assembly and flange-to-sensor distance tolerance.

8. The method as set forth in claim 1 wherein the step of determining the corrected position is based upon accessing calibration parameters stored in a memory operatively connected to the controller and located in the lens assembly.

9. The method as set forth in claim 1 , further comprising, receiving, from the vision system camera, a firmware update for storage in a memory operatively connected to the controller and located in the lens assembly when a current firmware version in the memory is out-of-date compared to a version stored by the vision system camera.

10. The method as set forth in claim 1 , further comprising, indicating when the lens position has moved to a corrected position.

11. A method for controlling focus of a membrane-based liquid lens assembly of a vision system camera comprising the steps of:
receiving, at a local controller mounted in a lens body containing the liquid lens assembly, a target focal distance provided by a vision system processor of the vision system camera;
determining, based on the target focal distance, a target position of an actuator of the membrane-based liquid lens assembly;
determining, based upon a position sensor associated with movement of the actuator, a current position of the actuator;
comparing the current position with the target position, and determining a corrected position that is associated with the target position; and
instructing movement of a position of the actuator to the corrected position.

12. The method as set forth in claim 11 , further comprising moving a membrane of the liquid lens assembly via movement of the position of the actuator.

13. The method as set forth in claim 11 , further comprising, correcting the target position based upon at least one of (a) a measured temperature of the liquid lens assembly, (b) a spatial orientation of the liquid lens assembly relative to an acting direction of gravity and (c) a stored sensor-to-flange distance tolerance associated with a mount of the lens body.

14. The method as set forth in claim 11 wherein the step of determining the current position comprises receiving a measurement value from a Hall sensor.

15. The method as set forth in claim 11 wherein the step of instructing movement comprises varying a current supplied to the actuator.

16. The method as set forth in claim 11 wherein the step of instructing movement comprises supplying a current to an annular bobbin assembly of the actuator.

17. The method as set forth in claim 11 further comprising receiving a temperature of the liquid lens assembly, and determining the corrected position using the received temperature.

18. The method as set forth in claim 11 further comprising receiving a spatial orientation of the liquid lens assembly, and determining the corrected position using the received spacial orientation.

19. The method as set forth in claim 18 , wherein the spatial orientation is received from an accelerometer associated with the vision system camera.

Assignees

• Cognex Corp

Inventors

• Nunnink Laurens
• Delasauce Rene
• Equitz William

Classifications

• G02B7/38

  measured at different points on the optical axis {, e.g. focussing on two or more planes and comparing image data} · CPC title

• G02B7/08 Primary

  adapted to co-operate with a remote control mechanism · CPC title

• G02B3/14

  of variable focal length · CPC title

• G02B7/30

  using parallactic triangle with a base line · CPC title