Method and apparatus for calibrating a measurement system
View Patent ↗A method and apparatus for calibrating a measurement system are provided. The method and apparatus compensate not only for lamp variations, but also for camera and optics variations. The system can be readily implemented and can be ported from one measurement system to another. One embodiment of the improved calibration system addresses the issue of variations between light sources by employing an automated lamp calibration system. One method calibrates existing or new lamps to match an established standard. In a preferred embodiment, the method will generate a reference table, for a measurement system defined as the standard, to act as the reference for all measurement systems. The reference table may be in the form of a data file that may be subsequently copied to other measurement systems. The reference table can then act as a global standard for other measurement systems, including future systems not yet made.
1. A method of generating a calibration file for use with a measurement system, the method comprising performing a) through k) for each of a plurality of command signal setpoints:
a) generating a digital control value corresponding to the command signal setpoint;
b) converting the digital control value to a corresponding analog control value;
c) applying the analog control value to a light source whereby the intensity of the light source depends upon the analog control value;
d) measuring the intensity of the light source with an image capturing device;
e) providing a measured intensity value to a comparator;
f) determining a reference intensity value corresponding to the command signal setpoint;
g) providing the reference intensity value to the comparator;
h) comparing the reference intensity value to the measured intensity value;
i) if the measured intensity value is lower than the reference intensity value, then incrementally increasing the digital control value applied to the light source and repeating b).through h);
j) if the measured intensity value is higher than the reference intensity value, then incrementally decreasing the digital control value applied to the light source and repeating b) through h); and
k) if the measured intensity value is within the acceptable tolerances, then recording the current digital control value and the corresponding command signal setpoint in a calibration file.
2. A method according to claim 1 ,
wherein incrementally increasing the digital control value and repeating b) through h) further comprises increasing the digital control value by a fixed increment until the measured intensity value is greater than the reference intensity value and then reducing the amount of the fixed increment; and
wherein incrementally decreasing the digital control value and repeating b) through h) further comprises decreasing the digital control value by a fixed increment until the measured intensity value is lower than the reference intensity value and then reducing the amount of the fixed increment.
3. A method according to claim 1 wherein measuring the intensity of the light source further comprises:
generating an electronic image of a standard with a digital camera;
frame grabbing the electronic image;
digitizing the electronic image;
selecting a portion of the digitized electronic image; and
measuring the intensity of the selected portion of the digitized electronic image.
4. A method according to claim 1 further comprising:
providing a standard for measuring intensity of light; and
wherein measuring the intensity of the light source further comprises measuring an amount of light reflected from the surface of the standard.
5. A method according to claim 4 wherein the standard comprises a reflective glass surface.
6. A method according to claim 4 wherein the standard comprises an opaque object.
7. A method according to claim 4 wherein the standard comprises a diffuse surface.
8. A method according to claim 1 further comprising providing a neutral density filter between the light source and the image capturing device so as to prevent saturation of the image capturing device.
9. A method according to claim 8 wherein providing a neutral density filter is performed in response to an instruction within a reference table.
10. A computer program product operable to calibrate the operation of a precision measurement instrument, the computer program product comprising a computer memory encoded with instructions for performing the a) through k) for each of a plurality of command signal setpoints:
a) generating a digital control value corresponding to the command signal setpoint;
b) converting the digital control value to a corresponding analog control value;
c) applying the analog control value to a light source whereby the intensity of the light source depends upon the analog control value;
d) measuring the intensity of the light source with an image capturing device;
e) providing a measured intensity value to a comparator;
f) determining a reference intensity value corresponding to the command signal setpoint;
g) providing the reference intensity value to the comparator;
h) comparing the reference intensity value to the measured intensity value;
i) if the measured intensity value is lower than the reference intensity value, then incrementally increasing the digital control value applied to the light source and repeating b) through h);
j) if the measured intensity value is higher than the reference intensity value, then incrementally decreasing the digital control value applied to the light source and repeating b) through h); and
k) if the measured intensity value is within the acceptable tolerances, then recording the current digital control value and the corresponding command signal setpoint in a calibration file.
11. A computer program product according to claim 10 ,
wherein the instructions for incrementally increasing the digital control value and repeating b) through h) further comprise increasing the digital control value by a fixed increment until the measured intensity value is greater than the reference intensity value and then reducing the amount of the fixed increment; and
wherein the instructions for incrementally decreasing the digital control value and repeating b) through h) further comprise decreasing the digital control value by a fixed increment until the measured intensity value is lower than the reference intensity value and then reducing the amount of the fixed increment.
12. A computer program product according to claim 10 wherein the instructions for measuring the intensity of the light source further comprise:
frame grabbing an electronic image generated by the image capturing device;
digitizing the electronic image;
selecting a portion of the digitized electronic image; and
measuring the intensity of the selected portion of the digitized electronic image.
13. A computer program product according to claim 10 further comprising instructions for prompting an operator to provide a neutral density filter between the light source and the image capturing device in response to an instruction within a reference table.