DRAFTING WITH LIGHT
This thesis describes the method of selection and implementation of a drafting device suitable for use with a high quality precision automatic drafting system intended for the production of navigational charts. This drafting system consists of a minicomputer for control (1), an industry compatible magnetic tape transport for data input (2), and a precision flatbed drafting table. After consideration of various methods, a technique was selected in which a beam of light is used to expose photosensitive material. Lines are drafted by moving the beam across the film. Symbols are produced by shaping the beam into the desired configuration and flashing it onto the film. An optical mechanical light head, made by Barr and Stroud Limited, was chosen as being most suitable but it was necessary to design the control and interface for its interconnection with the plotter and the minicomputer. Particular emphasis was placed on the use of stepper motor positioning controls as being most compatible with digital control circuitry and on the best method of controlling light intensity for varying drafting speeds on film. This entailed a detailed study of the properties of light sources, films and optical systems as well as control circuitry. The final interface and control unit that was constructed for the Barr and Stroud light head is described. This is followed by an analysis of the performance of the light head in its working environment. This research was supported by the Canadian Hydrographic Service, Marine Sciences Branch.