Patent ID: 9067445
Filing Date: 2015-06-30
Classification: B41J

Abstract:
1. A method for calibrating a printhead in a printer comprising: operating a printhead with a controller to eject a plurality of ink drops from an inkjet in a printhead to form a plurality of marks on an image receiving surface of a print medium moving past the printhead in a process direction, each mark extending in the process direction on the image receiving surface; generating with an optical sensor image data of a predetermined portion of the image receiving surface that includes the plurality of marks, the image data including a two-dimensional arrangement of pixels with a plurality of pixel rows extending in a cross-process direction and a plurality of pixel columns extending in the process direction; identifying with the controller a plurality of amplitudes, each amplitude being identified for a portion of each pixel column in the image data of the predetermined portion of the image receiving surface, the portion of each pixel column including expected locations for a portion of the plurality of printed marks in the process direction; identifying with the controller a pixel column corresponding to one of the plurality of identified amplitudes having an absolute value that is a local maximum within the image data for the predetermined portion of the image receiving surface; identifying with the controller a cross-process direction location of the inkjet that ejected the ink drops in the identified pixel column with reference to the identified pixel column; storing with the controller the identified cross-process direction location of the inkjet in a memory for use in printhead registration; identifying with the controller a first sum of a plurality of products formed by multiplying the image data pixel values in the identified pixel column by a sine function corresponding to the printed pattern of marks in the pixel column; identifying with the controller a second sum of a plurality of products formed by multiplying the image data pixel values in the identified pixel column multiplied by a cosine function corresponding to the printed pattern of marks in the pixel column; identifying with the controller an offset with reference to an arc tangent of a ratio of the identified first sum divided by the identified second sum; identifying with the controller an average location of the printed marks in the process direction with reference to the offset, a predetermined number of the printed marks, and a predetermined dimension in the process direction for each printed mark in the plurality of printed marks; and storing with the controller the average location of the printed marks in the memory for identification of a process direction location of printed ink drops ejected from the inkjet.