Autofocus barcode scanner and the like employing micro-fluidic lens

A method of operating a machine-readable symbol reader to read machine-readable symbols carried by targets, the method comprising:

• determining a distance between a microfluidic lens assembly of the machine readable symbol reader and the target;
• adjusting a focal length of the microfluidic lens assembly based on the determined distance to the target, wherein adjusting a focal length of the microfluidic lens assembly includes:
• applying a first potential to at least one of a number of electrodes spaced from a substantially non-conducting fluid by a dielectric;
• and
• applying a second potential to a substantially conducting fluid surrounding the first fluid, where the non-conducting fluid and the conducting fluid are immiscible with respect to one another;
• capturing an image of a machine-readable symbol carried by the target;
• and
• decoding the machine-readable symbol carried by the target.

A method of operating a machine-readable symbol reader to read color encoded machine-readable symbols carried by targets, the method comprising:

• acquiring an image through a three color filter at a single optical sensor;
• determining a plurality of sub-windows of the image on which to operate;
• for each of the colors, determining a subtraction-modulus-difference value for each of a number pixels in horizontally adjacent ones of the sub-windows and for each of a number pixels in vertically adjacent ones of the sub-windows;
• accumulating the subtraction-modulus-difference value for each of at least three different colors;
• aggregating adjacent sub-windows having accumulated subtraction-modulus-difference values below a defined threshold into a meta window of the image on which to operate;
• determining a focus value corresponding to a focus condition at an initial focal length of the microfluidic lens assembly;
• adjusting the microfluidic lens assembly to a second focal length;
• determining a focus value corresponding to a focus condition at the second focal length of the microfluidic lens assembly;
• determining a direction of change in the determined focus values;
• repeatedly, adjusting the microfluidic lens assembly at different incremental focal lengths in a space of the image along the same direction in the space, and
• determining a focus value corresponding to a focus condition at the different incremental focal lengths until the focus value drops by more than a defined threshold;
• and
• interpolating a best focus length from at least three of the focal lengths.

A machine-readable symbol reader to read machine-readable symbols carried by targets, the machine-readable symbol reader comprising:

• a microfluidic lens assembly having at least one first fluid and a number of electrodes selectively operable to modify a shape of the at least one first fluid;
• an optical sensor positioned along an optical axis of the microfluidic lens assembly relatively behind the microfluidic lens assembly with respect to the target;
• at least one controller, the controller coupled to cause a selected potential to be applied to at least some of the electrodes of the microfluidic lens assembly to focus images of the target on the optical sensor;
• and
• wherein at least one optical interface element of the lens comprises a second fluid, the first and the second fluids being immiscible fluids of different optical indexes and of substantially same density with second fluid being substantially electrically-conductive and the first fluid being substantially electrically-non-conductive.

A method of operating a machine-readable symbol reader to read machine-readable symbols carried by targets, the method comprising:

• determining a distance between a microfluidic lens assembly of the machine readable symbol reader and the target;
• adjusting a focal length of the microfluidic lens assembly based on the determined distance to the target;
• capturing an image of a machine-readable symbol carried by the target;
• decoding the machine-readable symbol carried by the target;
• and
• identifying the target in an image before determining the distance between a microfluidic lens assembly of the machine readable symbol reader and the target, wherein identifying the target in an image before determining the distance between a microfluidic lens assembly of the machine readable symbol reader and the target includes:
• determining a plurality of sub-windows of the image on which to operate;
• determining a subtraction-modulus-difference value for each of a number pixels in horizontally adjacent ones of the sub-windows and for each of a number pixels in vertically adjacent ones of the sub-windows;
• aggregating adjacent sub-windows having determined subtraction-modulus-difference values below a defined threshold into a meta window of the image on which to operate;
• determining a focus value corresponding to a focus condition at an initial focal length of the microfluidic lens assembly;
• adjusting the microfluidic lens assembly to a second focal length;
• determining a focus value corresponding to a focus condition at the second focal length of the microfluidic lens assembly;
• determining a direction of change in the determined focus values;
• repeatedly, adjusting the microfluidic lens assembly at different incremental focal lengths in a space of the image along the same direction in the space, and
• determining a focus value corresponding to a focus condition at the different incremental focal lengths until the focus value drops by more than a defined threshold;
• and
• interpolating a best focus length from at least three of the focal lengths.