Faulty nozzle detection in an ink jet printer by printing test patterns and scanning with a fixed optical sensor

An apparatus for detecting faulty nozzles in an ink jet printer comprising:

• processor means for receiving print data and for generating print commands, scan commands, and advance commands based on the print data;
• an ink jet print head comprising a plurality of ink jet nozzles disposed adjacent a print medium, the print head for receiving the print commands from the processor means and for ejecting ink droplets from each of the nozzles in response to the print commands, thereby printing individual test images on the print medium corresponding-to each nozzle, where each test image is formed from ink ejected from one corresponding nozzle, the print head for printing the test images at test image positions that are substantially aligned in a single column on the print medium;
• a printed image sensor positioned adjacent the print medium and having,a field of view intersecting the column of test image positions on the print medium, the field of view coinciding with only one test image position at a time, the printed image sensor for detecting individual ones of the test images printed on the print medium as the test image positions advance individually and sequentially through the field of view, and for generating a sensor signal indicating a first state when the printed image sensor detects one of the test images, and indicating a second state when the printed image sensor does not detect one of the test images, the printed image sensor being nonmovable in a direction perpendicular to the column of test images;
• a print medium advance mechanism for moving the print medium to cause the test positions on the print medium to move sequentially and individually through the field of view of the printed image sensor;
• the processor means further for receiving the sensor signal from the printed image sensor, for determining when the printed image sensor is adjacent a test image position, for generating a fault signal when the printed image sensor is adjacent a test image position and the sensor signal does not indicate the first state, for identifying which of the nozzles is faulty based on the reference distance between the reference position and the test image position corresponding to the faulty nozzle, and for generating an identification signal indicative of which of the nozzles is faulty;
• a status array memory device for storing a status array comprising status values which are indicative of a condition of each of the plurality of nozzles;
• the processor means further for updating the status-array based on the identification signal;
• and
• a printer driver for accessing the status array memory device, for determining which of the plurality of nozzles are not faulty based on the status array, and for generating print data for activating only the nozzles that are not faulty, where print data that would be directed to a faulty nozzle is rerouted to a nozzle that is not faulty.

A method for detecting faulty nozzles in a print head of an ink jet printer, where the ink jet printer forms printed images on a print medium by ejecting ink droplets from the nozzles as the print head scans across the print medium in a horizontal direction, the printer including an optical sensor for sensing the printed images on the print medium, and including a print medium advance mechanism for moving the print medium in vertical direction, the method comprising the steps of:

• (a) forming a test image on the print medium at a corresponding test position, the test image formed by ejecting ink droplets from a corresponding one of the nozzles;
• (b) moving the print medium in the vertical direction to leave a nonprinted area;
• (c) repeating steps (a) and (b) for each remaining nozzle on the print head to form on the print medium a single column of test images that are substantially aligned in the vertical direction;
• (d) maintaining a limited field of view of the optical sensor such that the field of view intersects no more than one of the test positions at a time while remaining consistently aligned with the column of test positions;
• (e) moving the print medium in the vertical direction relative to the optical sensor, thereby causing the test images and nonprinted areas to move individually and sequentially through the field of view of the optical sensor;
• (f) individually detecting the test images and the nonprinted areas using the optical sensor while maintaining the optical sensor in a fixed position relative to the horizontal direction as the print medium is moved in the vertical direction relative to the optical sensor;
• (g) generating a sensor signal with the optical sensor based on the detecting, the sensor signal indicating a first state when one of the test images is detected, and indicating a second state when one of the nonprinted areas is detected;
• (h) determining whether the field of view of the optical sensor is intersecting one of the test positions as the print medium is moved in the vertical direction relative to the optical sensor;
• (i) generating a fault signal when the field of view of the optical sensor is intersecting one of the test positions and the sensor signal does not indicate the first state;
• (j) identifying which of the nozzles is faulty based at least in part on the fault signal;
• and
• (k) compensating for one or more nozzles that are faulty.

A method for detecting faulty nozzles in a plurality of nozzles in a print head of an ink jet printer, where the ink jet printer forms printed images on a print medium by ejecting ink droplets from the plurality of nozzles as the print head scans across the print medium in a first direction, the printer including an optical sensor having a field of view for sensing the printed images on the print medium, and including a print medium advance mechanism for moving the print medium in second direction that is substantially orthogonal to the first direction, the method comprising the steps of:

• (a) forming a test image on the print medium at a corresponding test position, the test image formed by ejecting ink droplets from a corresponding one of the nozzles;
• (b) moving the print medium in the second direction to leave a nonprinted area;
• (c) repeating steps (a) and (b) for each remaining nozzle on the print head to form on the print medium a single column of test images that are substantially aligned in the second direction;
• (d) moving the print medium relative to the optical sensor, thereby causing the test positions to move individually through the field of view of the optical sensor;
• and
• (e) generating a fault signal when the field of view of the optical sensor intersects any one of the test positions and the optical sensor does not sense a test image.