Dynamic focus calibration, such as dynamic focus calibration using an open-loop system in a bar code scanner

Abstract

A system and method for recalibrating a bar code scanner or other optical system is described. In some cases, the system dynamically adjusts the focal length of a lens assembly based on open-loop process, such as based on feedback related to a distance between the lens assembly and an imaged object. In some cases, the system dynamically adjusts the lens assembly in order to provide auto focusing or zoom adjustment

1 . A method of dynamically recalibrating a bar code reader, the method comprising:
 receiving a recalibration signal or an indication of an error in reading an image of a machine readable code imaged by the bar code reader using a lens assembly calibrated at a first focal length, wherein the bar code reader employs open-loop auto focus controls;   measuring a distance between the machine readable code and a lens assembly in the bar code scanner, wherein the distance is measured with a range finder carried by the bar code scanner;   determining a second focal length of the lens assembly that provides a better image of the machine readable code; and   recalibrating the open-loop auto focus controls of the bar code reader using the determined second focal length and the measured distance.   
   
   
       2 . The method of  claim 1 , wherein measuring the distance between the machine readable code and the lens assembly comprises triangulating an output signal of the range finder. 
   
   
       3 . The method of  claim 1 , wherein recalibrating the bar code reader comprises adjusting a look-up-table with the determined second focal length and the measured distance and applying the look-up-table to an actuator of the lens assembly that controls the focal length of the lens assembly. 
   
   
       4 . The method of  claim 1 , wherein recalibrating the bar code reader comprises adjusting a parametric equation based at least in part on the determined second focal length and the measured distance and applying a parametric equation to an actuator of the lens assembly that controls a focal length of the lens assembly. 
   
   
       5 . The method of  claim 1 , further comprising:
 measuring a second distance between the machine readable code and the lens assembly in the bar code reader, wherein the second distance is measured from a different position with respect to the machine readable code; and   determining a third focal length of the lens assembly that provides a better image of the machine readable code than the first focal length;   wherein recalibrating the bar code reader comprises using at least in part the third focal length and the measured second distance.   
   
   
       6 . The method of  claim 1 , wherein receiving a recalibration signal or an indication of an error comprises failing to decode the image of the machine readable code. 
   
   
       7 . The method of  claim 1 , wherein receiving a recalibration signal or an indication of an error comprises receiving the recalibration signal or the indication from a user of the bar code reader. 
   
   
       8 . The method of  claim 1 , wherein receiving a recalibration signal or an indication of an error comprises receiving the recalibration signal or the indication from an environmental sensor that measures characteristics of a location of the bar code reader. 
   
   
       9 . The method of  claim 1 , wherein receiving a recalibration signal or an indication of an error comprises receiving the recalibration signal or the indication from a temperature sensor that measures the temperature of the lens assembly of the bar code reader. 
   
   
       10 . The method of  claim 1 , wherein receiving a recalibration signal or an indication of an error comprises receiving the recalibration signal or the indication from an acceleration sensor that senses that a user of the bar code reader is shaking the reader. 
   
   
       11 . The method of  claim 1 , wherein receiving a recalibration signal or an indication of an error comprises automatically receiving the recalibration signal or the indication at a preset time. 
   
   
       12 . A hand-held device configured to take an image of an object, comprising:
 a lens assembly having an adjustable focal length;   a range finder, wherein the range finder determines a distance between the hand-held device and a position on a selected object;   an operation monitoring component, wherein the operation monitoring component receives an adjustment signal and initiates an adjustment of the focal length; and   a dynamic adjustment component coupled to the lens assembly and range finder, wherein the dynamic adjustment component adjusts the focal length of the lens assembly based on information received from the range finder and based on the received signal from the operation monitoring component.   
   
   
       13 . The device of  claim 12 , wherein the lens assembly comprises a liquid whose shape is determined based on a voltage applied to the liquid. 
   
   
       14 . The device of  claim 13 , wherein the lens assembly includes:
 a bottom plate, wherein the bottom plate includes a substrate layer, one or more electrodes, and a hydrophobic layer that provides a surface for the liquid; and   a top plate, wherein the top plate includes a substrate layer and an electrode;   wherein the bottom plate and top plate form a cavity that contains the liquid.   
   
   
       15 . The device of  claim 13 , wherein the lens assembly includes:
 an adjustable lens component containing the liquid; and   one or more additional lens components configured to provide a substantially infinite focus distance.   
   
   
       16 . The device of  claim 12 , wherein the dynamic adjustment component changes a transfer function that controls the focal length of the lens assembly. 
   
   
       17 . The device of  claim 12 , wherein the dynamic adjustment component changes one or more look-up-tables that control the focal length of the lens assembly. 
   
   
       18 . The device of  claim 12 , wherein the dynamic adjustment component changes one or more parametric equations that control the focal length of the lens assembly. 
   
   
       19 . The device of  claim 12 , further comprising:
 a focus optimization component, wherein the focus optimization component determines an optimum focus of the lens assembly by analyzing an image of the selected object;   wherein the dynamic adjustment component adjusts the focal length of the lens assembly at least in part based on information received from the focus optimization component.   
   
   
       20 . The device of  claim 12 , further comprising:
 a focus optimization component, wherein the focus optimization component determines an optimum focus of the lens assembly;   wherein the dynamic adjustment component adjusts the focal length of the lens assembly at least in part based on information received from the focus optimization component.   
   
   
       21 . The device of  claim 12 , wherein the adjustment signal is related to an error detected in operation of the device. 
   
   
       22 . The device of  claim 12 , wherein the adjustment signal is related to a periodic calibration of the device. 
   
   
       23 . The device of  claim 12 , wherein the operation monitoring component is configured to periodically initiate the adjustment of the focal length. 
   
   
       24 . The device of  claim 12 , wherein the operation monitoring component is configured to receive input from a user of the device. 
   
   
       25 . A computer memory within an imaging device and containing a data structure, the data structure used to calibrate the imaging device, the data structure comprising:
 one or more entries relating distance from an object to be imaged with the device and a lens of the device and a focal length to be applied to the lens of the device, wherein the distance is measured by an open-loop control process and the focal length is determined by a closed-loop process.   
   
   
       26 . The computer memory of  claim 25 , wherein the open-loop control process is a triangulation of an output beam emitted by the device. 
   
   
       27 . A system for dynamically recalibrating a bar code reader, the method comprising:
 means for receiving an indication of an error in reading an image of a machine readable code imaged by the bar code reader using a lens assembly calibrated at a focal length;   means for measuring a first distance and a second distance, wherein the first distance is a distance between a first position on a machine readable code and a lens assembly in the bar code reader and the second distance is a distance between a second position on a machine readable code and the lens assembly;   means for determining an alternate focal length of the lens assembly that provides an adjusted image of the machine readable code; and   recalibrating the bar code reader using the determined alternate focal length and the measured distances.   
   
   
       28 . A machine readable symbol reader configured to image a machine readable symbol, comprising:
 a lens assembly having an adjustable focal length;   an open-loop measurement component, wherein the open-loop measurement component determines a distance between the machine readable symbol reader and a position on a machine readable symbol;   a focus adjustment component, wherein the focus adjustment component determines an adjusted focus of the lens assembly; and   a dynamic adjustment component coupled to the lens assembly and open-loop measurement component, wherein the dynamic adjustment component adjusts the focal length of the lens assembly based on one or more determined distances and based on one or more focus adjustments.   
   
   
       29 . The reader of  claim 28 , wherein the open-loop measurement component comprises a range finder carried by the reader.