Vector Plotters

Aperture Wheels

Aperture wheels are used by vector plotters. The aperture wheel is a disk with 24 or 70 apertures arrayed radially along the circumference. When the plotter selects an aperture, the wheel is rotated to place the desired aperture between the light source and the film. The apertures themselves are pieces of film, and can be made to any shape required; this can be time-consuming and there are limitations on size.

Flash and Draw Apertures

To achieve constant exposure on a vector photo plotter, apertures used for flashing pads are filtered differently than those used for drawing traces. Therefore, Flash and Draw apertures cannot be used interchangeably without the risk of localized overexposure and underexposure.

Aperture Wheel Setup for Vector Plotters

The setup of an aperture wheel is an exacting and time consuming process since each aperture in the wheel must be hand-mounted and aligned. In order to avoid repeated setup costs, designers have the photo plotting vendor keep a wheel on file and are forced to always use that same set of apertures. This has obvious drawbacks, both in terms of design flexibility and the ease of migration to other vendors.