Method of controlling laser scanner phase in a multicolor electrophotographic machine

A method of aligning print images of an electrophotographic machine on a print medium, said method comprising the steps of:

• providing a first rotating photoconductive drum and a second rotating photoconductive drum in the electrophotographic machine, each said drum having a substantially equal surface speed;
• scanning a first laser beam across said first photoconductive drum to produce a first scan line in a scan direction;
• cyclically repeating said scanning of said first laser beam in a plurality of first scan cycles to thereby produce a plurality of substantially parallel said first scan lines on said first photoconductive drum, a first time duration of each said first scan cycle being a substantially equal and constant first scan cycle time period;
• applying a respective line of first toner to each of said first scan lines;
• scanning a second laser beam across said second photoconductive drum to produce a second scan line in the scan direction;
• cyclically repeating said scanning of said second laser beam in a plurality of second scan cycles to thereby produce a plurality of substantially parallel said second scan lines on said second photoconductive drum, a second time duration of each said second scan cycle being substantially equal to said first time duration;
• applying a respective line of second toner to each of said second scan lines;
• providing a toner transfer medium contacting each said photoconductive drum at a respective toner transfer nip, said toner transfer medium having a surface speed substantially equal to said surface speed of each of said photoconductive drums;
• adjusting a plurality of times at which said second laser beam starts respective said second scan lines to thereby achieve a desired time difference between a first point in time when said first laser beam starts a selected said first scan line and a second point in time when said second laser beam starts a selected said second scan line;
• said desired time difference being such that at least one said line of first toner is substantially aligned in a process direction with a corresponding said line of second toner on said toner transfer medium, said process direction being substantially perpendicular to said scan direction;
• transferring said toner from said photoconductive drums to said toner transfer medium;
• and
• transferring said toner from said toner transfer medium to the print medium.

A method of aligning print images of an electrophotographic machine on a print medium, said method comprising the steps of:

• providing a first rotating photoconductive drum and a second rotating photoconductive drum in the electrophotographic machine, each said drum having a substantially equal surface speed;
• scanning a first laser beam across said first photoconductive drum to produce a first scan line in a scan direction;
• cyclically repeating said scanning of said first laser beam in a plurality of first scan cycles to thereby produce a plurality of substantially parallel said first scan lines on said first photoconductive drum, a first time duration of each said first scan cycle being a substantially equal and constant first scan cycle time period;
• applying a respective line of first toner to each of said first scan lines;
• scanning a second laser beam across said second photoconductive drum to produce a second scan line in the scan direction;
• cyclically repeating said scanning of said second laser beam in a plurality of second scan cycles to thereby produce a plurality of substantially parallel said second scan lines on said second photoconductive drum, a second time duration of each said second scan cycle being substantially equal to said first time duration;
• applying a respective line of second toner to each of said second scan lines;
• providing a toner transfer medium contacting each said photoconductive drum at a respective toner transfer nip, said toner transfer medium having a surface speed substantially equal to said surface speed of each of said photoconductive drums;
• generating a first synchronization signal indicating a plurality of first times at which said first laser beam starts a respective said first scan line;
• generating a second synchronization signal indicating a plurality of second times at which said second laser beam starts a respective said second scan line, said second signal being time staggered relative to said first signal such that at least one said line of first toner is substantially aligned in a process direction with a corresponding said line of second toner on said toner transfer medium, said process direction being substantially perpendicular to said scan direction;
• modulating said first laser beam during said scanning step and dependent upon said first synchronization signal;
• modulating said second laser beam during said scanning step and dependent upon said second synchronization signal;
• transferring said toner from said photoconductive drums to said toner transfer medium;
• and
• transferring said toner from said toner transfer medium to the print medium.

A method of providing image registration in an electrophotographic printer having a plurality of multi-faceted mirrors and a corresponding plurality of developing units having a corresponding plurality of toner transfer nips, said method comprising the steps of:

• reflecting a first laser beam off of a first of said mirrors, said first mirror rotating relative to said first laser beam to thereby scan said first laser beam across a first of said developing units to produce a first scan line in a scan direction;
• cyclically repeating said relative rotation between said first laser beam and said first mirror to thereby produce a plurality of substantially parallel said first scan lines on said first developing unit;
• applying a respective line of first toner to each of said first scan lines;
• reflecting a second laser beam off of a second of said mirrors, said second mirror rotating relative to said second laser beam to thereby scan said second laser beam across a second of said developing units to produce a second scan line in the scan direction;
• cyclically repeating said relative rotation between said second laser beam and said second mirror to thereby produce a plurality of substantially parallel said second scan lines on said second developing unit;
• applying a respective line of second toner to each of said second scan lines;
• providing a moving toner transfer medium contacting each of said first developing unit and said second developing unit at a respective said toner transfer nip;
• transferring each said line of first toner from said first photoconductive drum to said toner transfer medium;
• transferring each said line of second toner from said second photoconductive drum to said toner transfer medium such that said lines of second toner are substantially interspersed with said lines of first toner on said toner transfer medium;
• and
• providing a rotational offset of said second mirror relative to said first mirror, said rotational offset being such that at least one said line of first toner is substantially aligned in a process direction with a corresponding said line of second toner on said toner transfer medium, the process direction being substantially perpendicular to the scan direction.

A method of controlling the relative phase between a first laser scanner having a first polygonal mirror rotatably coupled to a first motor and a second laser scanner having a second polygonal mirror rotatably coupled to a second motor in an electrophotographic machine, comprising the steps of:

• setting a desired range of a phase difference between said first laser scanner and said second laser scanner;
• generating a first cyclical speed control signal for controlling a rotational velocity of said first laser scanner;
• generating a second cyclical speed control signal for controlling a rotational velocity of said second laser scanner;
• verifying that each of said first motor and said second motor is operating at a respective desired speed;
• measuring an actual phase difference between said first laser scanner and said second laser scanner;
• ascertaining whether said actual phase difference is within said desired range;
• if said actual phase difference is within said desired range, taking no action;
• and
• if said actual phase difference is not within said desired range:
• changing a time duration of at least one cycle of at least one of said first cyclical speed control signal and said second cyclical speed control signal to thereby temporarily change a speed of rotation of at least one of said first polygonal mirror and said second polygonal mirror;
• and
• repeating said measuring, ascertaining and changing steps until said actual phase difference is within said desired range.