Patent ID: 7832822
Filing Date: 2010-11-16
Classification: B41J

Abstract:
1. An ink jet printing apparatus having a conveyance system for conveying a print medium along a first direction comprising: a first printing head of an ink jet type in which a plurality of printing elements are arranged in a second direction different from the first direction; a second printing head of an ink jet type in which a plurality of printing elements are arranged in the second direction, provided at a downstream side with respect to the first printing head in the first direction; a third printing head of an ink jet type in which a plurality of printing elements are arranged in the second direction, provided at a downstream side with respect to the second printing head in the first direction; a fourth printing head of an ink jet type in which a plurality of printing elements for ejecting yellow ink are arranged in the second direction, provided at a downstream side with respect to the third printing head in the first direction; a first pair of rollers, provided at a upstream side with respect to the first printing head, that nips and conveys the print medium; a second pair of rollers, provided between the first printing head and the second printing head with respect to the first direction, that nips and conveys the print medium; a third pair of rollers, provided between the second printing head and the third printing head with respect to the first direction, that nips and conveys the print medium; a fourth pair of rollers, provided between the third printing head and the fourth printing head with respect to the first direction, that nips and conveys the print medium; a fifth pair of rollers, provided at a downstream side with respect to the fourth printing head, that nips and conveys the print medium; a first Doppler speedometer that acquires a moving speed of the print medium at a position between the first printing head and one of the second pair of rollers; a second Doppler speedometer that acquires a moving speed of the print medium at a position between the second printing head and one of the third pair of rollers; a third Doppler speedometer that acquires a moving speed of the print medium at a position between the third printing head and one of the fourth pair of rollers; and a control unit that controls drive timings of the first, the second, the third, and the fourth printing heads, wherein the first printing head is driven based on a moving speed acquired by the first Doppler speedometer, the second printing head is driven based on a difference in the moving speeds acquired by the first and the second Doppler speedometers, the third printing head is driven based on a difference in the moving speeds acquired by the second and the third Doppler speedometers, and the fourth printing head is driven based on a moving speed acquired by the third Doppler speedometer, wherein a Doppler speedometer is not provided corresponding to the fourth printing head.