Image forming apparatus and recording medium for correcting dot position

An image forming apparatus comprising:

• an image carrier exposed by a light beam to form an image on the image carrier;
• a light source that generates the light beam emitted in accordance with image data in synchronization with a write clock;
• an optical scanner that executes scanning of the light beam in a main scanning direction on the image carrier by a plurality of reflection surfaces of a rotary polygon mirror rotationally driven by a rotary drive source;
• a reflection surface identifier that identifies each of the reflection surfaces of the rotary polygon mirror;
• a sub-scanning direction driver that relatively moves the image carrier and the light beam to each other in a sub-scanning direction orthogonal to the main scanning direction;
• a storage that stores a first jitter information of the light beam obtained by a measurement device before execution of a print job, wherein the first jitter information corresponds to a first scanning time up to each of a plurality of positions in the main scanning direction on each of the reflection surfaces of the rotary polygon mirror;
• a photodetector that detects scanning of the light beam at a start position and an end position in the main scanning direction;
• and
• a hardware processor that:
• generates a second jitter information based on a detection result of the photodetector after a start of the execution of the print job, wherein the second jitter information corresponds to according to a second scanning time from the start position to the end position in the main scanning direction on each of the reflection surfaces of the rotary polygon mirror in accordance with a detection result of the photodetector,
• corrects the first jitter information in accordance with based on a difference between the first jitter information and the second jitter information at an end of a corresponding reflection surface among each of the reflection surfaces to obtain a correction characteristic for a dot position shift on each of the reflection surfaces of the rotary polygon mirror, and
• changes the frequency of the write clock based on the correction characteristic,
• when a position in the main scanning direction is Xn, a dot position shift is Yn, and a slope an at each of n positions Xn in the main scanning direction is an =(Xn+1−Yn)/(Xn+1−Xn), approximates a position shift, based on the first jitter information by an approximation equation Yn =anXn, and
• when a dot position shift according to the first jitter information at an end position Xeos in the main scanning direction is Yeos, a dot position shift according to the second jitter information at the end position Xeos in the main scanning direction is Y′eos, and a slope a′n of an approximation equation of the correction characteristic is a′n=(Y′eos/Yeos)*an, approximates the correction characteristic by an approximation equation Y′=a′nXn, and changes the frequency of the write clock by a′n.

A non-transitory recording medium storing a computer readable image forming control program that controls an image forming apparatus, wherein

• the image forming apparatus comprises:
• an image carrier exposed by a light beam to form an image on the image carrier;
• a light source that generates the light beam emitted in accordance with image data in synchronization with a write clock;
• an optical scanner that executes scanning of the light beam in a main scanning direction on the image carrier by a plurality of reflection surfaces of a rotary polygon mirror rotationally driven by a rotary drive source;
• a reflection surface identifier that identifies each of the reflection surfaces of the rotary polygon mirror;
• a sub-scanning direction driver that relatively moves the image carrier and the light beam to each other in a sub-scanning direction orthogonal to the main scanning direction;
• a storage that stores a first jitter information of the light beam obtained by a measurement device before execution of a print job, wherein the first jitter information corresponds to a first scanning time up to each of a plurality of positions in the main scanning direction on each of the reflection surfaces of the rotary polygon mirror;
• a photodetector that detects scanning of the light beam at a start position and an end position in the main scanning direction;
• and
• a hardware processor that:
• generates a second jitter information based on a detection result of the photodetector after a start of the execution of the print job, wherein the second jitter information corresponds to a second scanning time from the start position to the end position in the main scanning direction on each of the reflection surfaces of the rotary polygon mirror,
• corrects the first jitter information based on a difference between the first jitter information and the second jitter information at an end of each of the reflection surfaces to obtain a correction characteristic for a dot position shift on each of the reflection surfaces of the rotary polygon mirror;
• and
• changes the frequency of the write clock and adjusts the phase of the write clock based on the correction characteristic.

A non-transitory recording medium storing a computer readable image forming control program that controls an image forming apparatus, wherein

• the image forming apparatus comprising:
• an image carrier exposed by a light beam to form an image on the image carrier;
• a light source that generates the light beam emitted in accordance with image data in synchronization with a write clock;
• an optical scanner that executes scanning of the light beam in a main scanning direction on the image carrier by a plurality of reflection surfaces of a rotary polygon mirror rotationally driven by a rotary drive source;
• a reflection surface identifier that identifies each of the reflection surfaces of the rotary polygon mirror;
• a sub-scanning direction driver that relatively moves the image carrier and the light beam to each other in a sub-scanning direction orthogonal to the main scanning direction;
• a storage that stores a first jitter information of the light beam obtained by a measurement device before execution of a print job, wherein the first jitter information corresponds to a first scanning time up to each of a plurality of positions in the main scanning direction on each of the reflection surfaces of the rotary polygon mirror;
• a photodetector that detects scanning of the light beam at a start position and an end position in the main scanning direction;
• and
• a hardware processor that:
• generates a second jitter information based on a detection result of the photodetector after a start of the execution of the print job, wherein the second jitter information corresponds to a second scanning time from the start position to the end position in the main scanning direction on each of the reflection surfaces of the rotary polygon mirror,
• corrects the first jitter information based on a difference between the first jitter information and the second jitter information at an end of each of the reflection surfaces to obtain a correction characteristic for a dot position shift on each of the reflection surfaces of the rotary polygon mirror, and
• changes the frequency of the write clock based on the correction characteristic;
• when a position in the main scanning direction is Xn, a dot position shift is Yn, and a slope an at each of n positions Xn in the main scanning direction is an =(Xn+1−Yn)/(Xn+1−Xn), approximates a position shift based on the first jitter information by an approximation equation Yn =anXn;
• and
• when a dot position shift according to the first jitter information at an end position Xeos in the main scanning direction is Yeos, a dot position shift according to the second jitter information at the end position Xeos in the main scanning direction is Y′eos, and a slope a′n of an approximation equation of the correction characteristic is a′n =(Y′eos/Yeos)*an, approximates the correction characteristic by an approximation equation Y′=a′nXn, and changes the frequency of the write clock by a′n.