1. Field of the Invention
The present invention relates to feeding of a recording medium in printers. More specifically, the present invention relates to control of line feeding of a recording medium in conjunction with print head nozzle firing so as to advance the recording medium for high resolution printing with a lower amount of line feeding motor steps.
2. Description of the Related Art
Line feeding in printers refers to the advancement of a recording medium through the printer during printing operations. During printing operations, the recording medium is fed through the printer by line feed rollers that are driven by a line feed motor controlled by a controller. The line feed motor and the line feed rollers are connected by a drivetrain so that as the line feed motor rotates, the line feed rollers also rotate. The recording medium is fed between the line feed rollers and pinch rollers and as the line feed rollers rotate, the recording medium is fed through the printer.
One type of line feed motor is known as a stepper motor. A stepper motor rotates in steps, i.e. stepped increments or pulses. Each increment or pulse corresponds to a predetermined amount (or phase) of rotation. Some of the most common stepper motors used in printers have stepped increments of 1.8° (corresponding to a 200 pulse motor where 200 pulses×1.8°=360°), 3.60 (corresponding to a 100 pulse motor), and 3.75° (corresponding to a 96 pulse motor). For each increment (pulse) that the line feed motor rotates, the line feed rollers also rotate and feed the recording medium a horizontal amount corresponding to the amount of rotation of the line feed rollers. The amount of rotation of the line feed rollers is determined by the drivetrain ratio employed between the line feed motor and the line feed rollers.
Conventionally, the drivetrain ratio has been set so that one pulse of the line feed motor advances the recording medium an amount equivalent to the maximum resolution of the printer. For example, where the maximum resolution of a printout of the printer is 600 dpi (dots per inch), the drivetrain ratio has been set so that one pulse of the line feed motor corresponds to a 600 dpi pitch line feed of the recording medium. Thus, the line feed ratio to obtain a 600 dpi resolution printout would be 1/600 (1 pulse equals 600 dpi advancement of the recording medium).
In order to obtain higher resolution printouts, such as a 1200 dpi printout, additional motor pulses are required. Consider, for example, a print head having 100 nozzles spaced at a 600 dpi pitch printing a 1200 dpi image. The print head performs two scans across the same scan area to perform 1200 dpi printing (a first scan printing at 600 dpi and a second scan also printing at 600 dpi after a 1200 dpi paper advancement). After the second scan, the paper is advanced to the end of the 100 nozzle printout. In order to advance the paper to the end of the 100 nozzle print, 200 pulses of the motor would be required (it takes 2 pulses to advance the paper one 600 dpi pixel, therefore it takes 200 pulses to advance the paper 100 pixels). The 200 pulses result in a slower line feed speed than would otherwise be required if less motor pulses were needed to advance the paper the same 100 pixel amount. Thus, what is needed is a way to increase the line feed speed at higher resolutions.
It has been proposed that, to increase the line feed speed, that the motor speed itself could be increased. However, higher resolution printouts also require a higher degree of accuracy of the motor. Faster and more accurate motors are expensive and increase the cost of the printer. Therefore, what is needed is a way to increase the line feed speed at higher resolutions and to maintain accuracy without a significant increase in the motor cost.