7.0 IMPLEMENTATION

7.15 Generalization of image rotator example

It is easy to see how the rotator example can be applied to position control devices:

The "normal operation" SLEWING and TRACKING states will be replaced with a single MOVING state.
When HALTED, it may be desirable to open the Delta Tau position loop and/or power off motors and/or apply brakes so as to avoid jitter at the level of one or two encoder counts.
For devices with discrete named positions, a "name Ť position" table must be maintained. This will be maintained as a file on the Unix side; this file will be loaded by the EPICS sequencer (which will also be able to save the current settings).

There are two approaches to handling multiple degrees of freedom:

use a custom sequence that understands the device, or
use a generic sequence per degree of freedom.

The latter approach is proposed for the two ADCs, each of which consists of two independently-controllable prisms. Higher-level code (above the sequences) will calculate the desired prism angles, as illustrated in Figure 7-16 on page 7-35.

FIGURE 7-16. Calculation of ADC prism angles

AO Software Design Book - 25 FEB 1997

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