2.3. Plotters. 2.3. Plotters. View surface like screen.
Usually higher resolution than a screen. (See Figure 2.9 a and
b.)
(1)Movable Pen: Pen is moved to X,Y co-ordinate with
pen up = move
or pen down = draw.
Pen is mounted on a structure that is moved by servo or
stepper motors. These turn a certain amount dependent on applied
voltage. ie 011001 may translate into 2.5 volts which may turn
motor 20 degrees clockwise.
As motor spindle rotates so pen moves in linear direction since connected by band. Similarly this spindle, band and pen assembly can be moved at right angles to give full X-Y positioning. Note that any slippage of band can produce a cumulative error.
Fig. 2.9 : Assembly for plotter and pen.
Circle may not join. Squares may not be repeatable.
Fig. 2.10 : Results of band or pen slippage
Many plotters allow different pens to be used ie different size or colour which can be changed in mid stream.
Flatbed plotters are large 10' x 5' flat surfaces and paper is held down electrostatically or by vacuum. Drum plotters have the paper wrapped around a drum which moves. Cheap plotters have the paper held down (badly) by metallic strips on a magnetic surface. This can reduce repeatability because paper can move or lift if not held down over its entire surface.
Fig. 2.11 : Example of plotter's resolution
Fig. 2.12 : Example of plotter's resolution
