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

摘要

An apparatus for detecting faulty nozzles in an ink jet printer includes an ink jet print head having a plurality of ink jet nozzles disposed adjacent a print medium. The print head prints a reference image on the print medium formed by ink droplets ejected from many of the nozzles. The print head also prints individual test images corresponding to each nozzle by ejecting ink droplets from each of the nozzles separately and sequentially. A print head scan mechanism scans the print head in a first direction relative to the print medium as the test images are printed. A print medium advance mechanism moves the print medium in a second direction between the printing of the reference image and the printing of the test images, where the second direction is orthogonal to the first direction. In this manner, the apparatus leaves nonprinted areas on the print medium between the reference image and the individual test images. A fixed optical sensor detects light reflected from the print medium and generates a sensor signal based thereon. The sensor signal indicates a first state when the sensor detects light reflected from a test image or from the reference image, and a second state when the sensor detects light reflected from a nonprinted area. When the optical sensor is adjacent a test image position and the sensor signal does not indicate the first state, the processor generates a fault signal.