Method of calibrating a contact image sensor scan bar in a document scanner

In a scanner having a scan bar calibration area and a CIS scan bar having an LED array for emitting N different colors of light where N≥3 and a sensor array having a plurality of photoreceptors, a method of calibrating the response of the sensor array, the method comprising:

• moving the CIS scan bar to the calibration area;
• illumining the LED array to emit a first color of light to reflect from the calibration area to illuminate the sensor array with the first color of light for a predetermined time period TP1;
• on the expiration of the time period TP1, determining whether or not an output signal of each photoreceptor is at a predetermined target value range;
• upon determining that the output signal of each photoreceptor is within the target value range, storing the measured time period TP1;
• upon determining that the output signal of each photoreceptor is not within the target value range, determining whether or not the time period TP1 is less than or equal to a predetermined line time;
• upon determining that the time period TP1 is not less than or equal to the predetermined line time, declaring a fault;
• and
• upon determining that the time period TP1 is less than or equal to the predetermined line time, increasing the time period TP1 by a second predetermined time period TP2, and returning to the step of illumining the LED array;
• repeating the foregoing steps for each remaining color of light and storing the respective time period TP1 for each remaining color of light;
• and
• creating for a color scan line cycle that is the sum of the stored time period TP1 for each respective color of light of the N different colors of light wherein, during scanning of an image, in the color scan line cycle, each respective color of light of the N different colors of light is emitted for its respective time period TP1.

In a scanner having a CIS scan bar having an LED array for emitting N different colors of light where N≥3 and a sensor array having a plurality of photoreceptors, a method of calibrating the response of the sensor array, the method comprising:

• initializing a target value and a line time LT to respective predetermined values;
• setting a safety margin SM to a predetermined multiplier value in the range of about 0.01 to about 0.25;
• illumining the LED array to emit a first color of light to reflect from a calibration target to illuminate the sensor array with the first color of light for a predetermined period of time TP1;
• on the expiration of the time period TP1, determining whether or not an output signal of each photoreceptor is at the predetermined target value;
• upon determining that the output signal of each photoreceptor is at the target value, setting the time period TP1=TP1+TP1*SM and storing the time period TP1;
• upon determining that the output signal of each photoreceptor is not within the target value, determining whether or not the time period TP1 is less than or equal to the line time LT;
• upon determining that the time period TP1 is not less than or equal to the line time LT, declaring a fault;
• and
• upon determining that the time period TP1 is less than or equal to the predetermined line time LT, increasing the time period TP1 by a second predetermined time period TP2, and returning to the step of illumining the LED array;
• for each remaining color of light repeating the foregoing steps and storing the respective TP1 for each color of light;
• and
• creating for a color scan line cycle that is the sum of the stored time period TP1 for each respective color of light of the N different colors of light wherein, during scanning of an image, in the color scan line cycle, each respective color of light of the N different colors of light is emitted for its respective time period TP1.