Method and apparatus for determining a process position of a scan line in an electrophotographic machine

An apparatus for determining a position of a laser beam in an electrophotographic machine, said apparatus comprising:

• a sensor device including a laser beam receiving surface having a first edge, a second edge and a third edge, said second edge being opposite from and nonparallel to said first edge, said third edge being parallel to said first edge, said sensor device being configured for transmitting at least one signal indicative of the laser beam intersecting said first edge, said second edge and said third edge during a scan of the laser beam in a scan direction;
• and
• a controller device configured for:
• receiving said at least one signal,
• measuring a first time period between said laser beam intersecting said first edge and said second edge,
• measuring a second time period between said laser beam intersecting said third edge and said first edge, and
• determining the position of the laser beam along a process direction substantially perpendicular to said scan direction, said determining being based upon a ratio between said measured first time period and said measured second time period.