The detection of the special commands inserted into the IBM re-
cord by the previewer will cause the programmer to stop the sequence at
the appropriate time and request the operator to assist in positioning the
image, or to add new image constants.
PLATE PREVIEWER SYSTEM
The components proposed for the previewer system are discussed in de-
tail from the point of view of the requirements to be met and the suitability
of the proposed solutions in meeting or exceeding the requirements. Since
the plate previewer is not generally intended to function independently,
consideration has been given at all times to the compatibility of its output
record with the requirements of the following high accuracy comparator.
From the point of view of accuracy and reliability, for example, such
considerations dictate the necessity of minimizing the error in the rough
coordinate readout to provide the most favorable conditions for the auto-
matic centering equipment in the comparator. From the point of view of
ease of operation and flexibility, they suggest the desirability of similar
concepts of operation, metering, and control in the two systems, differ-
ing only in the ultimate accuracy required of each system.
Basic Mechanism
1. General Requirements
The basic measuring table mechanism, upon which all other ac-
curacies depend, must provide straightness of x and y axis motion, plus
mutual perpendicularity, such that the maximum possible combined error,
plus errors from other sources, does not exceed the input capability of
the high accuracy comparator. This maximum table error, plus other er-
rors in the previewer, will be less than . 05 mm. at any point, in the Link
equipment,
The mechanism must contain a drive system which will permit
accurate positioning of the table with a minimum of operating fatigue and
lost time. This system must be protected by limit stops, safety switches,
and slip clutches to avoid damage to the mechanism,
A rotary platform must be provided with smooth action and fine
control to provide for accurate alignment of the fiducial marks relative to
carriage travel,
Finally, the mechanism must show a minimum instability due
to thermal effects. Careful choice of materials will ensure compatible