Optical sensor for plotter pen verification

An optical sensor for monitoring plotter pen performance by sensing the quality of lines drawn on a medium comprising:

• a pen carriage having a holder for removably mounting a pen;
• light source means mounted on said pen carriage for generating a beam of light sufficiently wide to illuminate a point on an underlying line drawn by the pen as well as the area on both sides of the line adjacent to the point;
• attachment means on said pen carriage for holding said light source means;
• an optical sensor also mounted on said pen carriage with the axis of said optical sensor positioned at an angle relative to said light source means and with both said optical sensor and said light source having their axes in non-perpendicular relationship to the surface of the medium;
• drive means for moving said light source means and said optical sensor across the underlying line to measure the print contrast ratio of the point on the line with its surrounding white background;
• and
• circuit means connected to said light source means and said optical sensor for activating said light source means and for processing a signal generated by said optical sensor and based on said print contrast ratio.