Portable "T"-configured X-Y plotter

A portable, X-Y plotter capable of plotting on any sized medium and work surface comprises a generally T-configured instrument transport assembly for controllably imparting a dual (X-Y) axis translation to an instrument (e.g. plotting pen) across a workpiece (paper) and controllably engaging the plotting pen with the paper during its translation. The transport assembly includes a first, generally cylindrical translation arm, which forms the top of the T-configuration and extends in a first axial direction. This first translation arm is supportable at its opposite ends on a work surface, such as a table top, upon which plotting paper is disposed. A second, generally cylindrical translation arm, which forms the vertical leg of the T, is coupled through a T-joint coupler to the first translation arm, so that the second translation arm extends in a second axial direction, orthogonal to said first axial direction. The opposite end of the second translation arm free wheels on the support surface. A plotting pen holder, which retains a plotting pen for controllable engagement with the paper, is mounted on the second translation arm for translational movement in the second direction. A dual stepper motor unit in the T-joint coupler drives a rack and pinion for the first arm and a drive belt for the pen holder. For optimal high speed operation, the stepper motors are ramped up to maximum speed, and then ramped down to avoid pen overshoot.