Image forming apparatus and control method thereof

An image forming apparatus comprising:

• an image forming unit to form a color registration error detection pattern on a photoconductor;
• a transfer unit to transfer the color registration error detection pattern formed on the photoconductor to a transfer belt;
• a pattern sensing unit to sense the color registration error detection pattern transferred to the transfer belt;
• a motor drive unit to drive a motor used to rotate the photoconductor;
• a control unit to ascertain a gap change of the color registration error detection pattern, which denotes a periodic velocity change of the photoconductor, by sensing the color registration error detection pattern transferred to the transfer belt, and to change a velocity of the motor according to the gap change to reduce the periodic velocity change of the photoconductor;
• a home-position sensing unit to sense a home-position of the photoconductor,
• wherein, if the home-position of the photoconductor is sensed while changing the velocity of the motor according to the gap change, the motor velocity change is reset and restarted by the control unit, to prevent error accumulation.

A control method of an image forming apparatus comprising:

• forming a color registration error detection pattern on a photoconductor;
• transferring the color registration error detection pattern formed on the photoconductor to a transfer belt;
• sensing the color registration error detection pattern transferred to the transfer belt;
• ascertaining a gap change of the color registration error detection pattern, which denotes a periodic velocity change of the photoconductor;
• and
• changing a velocity of a motor used to rotate the photoconductor according to the gap change,
• wherein the formation of the color registration error detection pattern on the photoconductor is performed on the basis of a time when a home-position of the photoconductor is sensed.

A control method of an image forming apparatus comprising:

• forming a color registration error detection pattern on a photoconductor;
• transferring the color registration error detection pattern formed on the photoconductor to a transfer belt;
• sensing the color registration error detection pattern transferred to the transfer belt;
• ascertaining a gap change of the color registration error detection pattern, which denotes a periodic velocity change of the photoconductor;
• and
• changing a velocity of a motor used to rotate the photoconductor according to the gap change,
• wherein the change of the velocity of the motor according to the gap change includes calculating a linear velocity function of the photoconductor from the gap change, calculating a motor velocity function from the linear velocity function of the photoconductor, and changing the velocity of the motor according to the motor velocity function, and
• the linear velocity function of the photoconductor is represented by the following equation if the gap change is a sine function:
• Photoconductor Linear Velocity Function=Vo+ωA cos(ωt+θ), where Vo is an average velocity of the photoconductor, A is a change magnitude, ω is an angular velocity 2πf, f is a velocity change frequency, and θ is a phase.

A method of reducing color registration error in an image forming apparatus comprising:

• determining a gap change of a color registration error detection pattern caused by a linear velocity change of a photoconductor;
• and
• performing an Auto Color Registration (ACR) operation for an image formed on the photoconductor to reduce the linear velocity change of the photoconductor based on a relationship between the gap change and a velocity of a motor,
• wherein the ACR operation comprises
• (a) driving the motor at a constant velocity;
• (b) confirming if a home-position of the photoconductor is sensed;
• (c) forming the color registration error detection pattern on the photoconductor;
• (d) transferring the color registration error detection pattern formed on the photoconductor to an intermediate transfer belt;
• (e) sensing the color registration error detection pattern transferred to the intermediate transfer belt;
• (f) determining if operations (a)-(e) are repeatedly performed a predetermined number of times or more;
• (g) calculating a gap difference between the bar-shaped patterns of the color registration error detection pattern if implementation of the operations (a)-(e) is determined to have been performed a predetermined number of times or more;
• (h) fitting the calculated gap difference of the color registration error detection pattern using model fitting to approximate the gap difference to a sine function;
• (i) estimating an amplitude and a phase of a gap change function via the fitting operation;
• (j) calculating a linear velocity of the photoconductor using the estimated amplitude and phase of the gap change function;
• (k) calculating a velocity of the motor using the calculated linear velocity of the photoconductor;
• and
• (l) changing the velocity of the motor based on the calculated velocity of the motor.