Plotter platen mapping system

In a graphics plotter wherein paper is moved over a platen, the method of positioning a pen at known distances form the paper surface as the pen is moved across the platen comprising the steps of:

• (a) measuring the deviation of the platen from parallel to a straight reference line at a plurality of spaced measurement points across the platen;
• (b) storing deviation values at the spaced points;
• and,
• (c) adjusting the desired position of the pen by the respective deviation values as the pen is moved across the platen between the measurement points.

In a graphics plotter system having a platen over which paper is moved longitudinally to create one axis, penholding apparatus moved transversely across the platen and the paper to create the other axis, and a controlled raising and lowering mechanism connected to the penholding apparatus for lowering a pen being held therein into contact with and for raising it from contact with the paper and for providing a relative vertical position value signal, the method of pen height control during pen movement comprising the steps of:

• (a) raising the pen to a full up position;
• (b) moving the pen towards the next pen down location;
• (c) while the pen is moving and prior to reaching the next pen down location beginning to lower the pen at a pre-established horizontal distance from the next pen down location and continuing to lower the pen as it is moving toward its next pen down position such that the pen ramps downward and attains a pre-established minimum clearance distance just as it arrives at the next pen down location;
• and,
• (d) lowering the pen through the minimum clearance distance to a full down position at the next pen down location.

In a graphics plotter system having a platen over which paper is moved longitudinally to create one axis, penholding apparatus moved transversely across the platen and the paper to create the other axis, and a controlled raising and lowering mechanism connected for rotating the penholding apparatus to lower a pen being held therein into contact with and to raise it from contact with the paper and for providing a relative vertical position value signal, the method of pen positional compensation comprising the steps of:

• (a) mapping deviations from a parallel relationship between the platen and the penholding apparatus at a plurality of spaced points across the width of the platen;
• (b) for each pen position calculating the difference in the actual position the pen will contact the platen and the desired position for pen contact as a function of the deviation at the desired position and the arc of movement of the penholding apparatus in lowering the pen;
• and,
• (c) adjusting the position at which the pen is positioned for lowering by the calculated difference so that the actual position the pen will contact the platen is the same as the desired position for pen contact.