Patent ID: 6042281
Filing Date: 2000-03-28
Classification: B41J

Abstract:
A printing apparatus comprising:a print head which is driven along a guide;a linear encoder comprising a scale which is in parallel to said guide, and a sensor which is driven along said scale together with said print head to read said scale and output a plurality of encoder output signals having different phases;position information signal generating means for generating a print position information signal indicating position of said print head by processing said encoder output signals; andhead drive means for driving said print head based on the position information signal output from said position information signal generating means and image data,wherein said position information signal generating means comprises:interpolating means for generating a reference pulse signal by detecting pulse edges in at least one of the encoder output signals output from said linear encoder, for obtaining interval data by measuring time periods between pulses in the reference pulse signal, for obtaining divided time data by dividing the interval data by a predetermined number, for generating a correction signal at each end of the time periods represented by the divided time data, and for outputting a first position information signal based on the correction signal and the reference pulse signal;an edge detector for outputting a second position information signal which is obtained by detecting pulse edges in the plurality of encoder output signals, generating pulses in response to the edge detection, and synthesizing the detection pulses;selecting means for selecting one of the first position information signal from said interpolating means and the second position information signal from said edge detector; andselect control means for controlling said selecting means to select the first position information signal from said interpolating means as the print position information signal when said print head is driven at a speed which is higher than a speed control limit and to select the second position information signal from said edge detector as the print position information signal when said print head is driven at a speed which is lower than the speed control limit.