Closed-Loop Operation; Servo Loop - Newport New Focus Picomotor 8743-CL User Manual

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3.3

Closed-Loop Operation

The Model 8743-CL can operate in an open-loop mode with either closed-loop or open-
loop Picomotors. In addition, it can operate in closed-loop mode when connected to
closed-loop Picomotors. The unit will also support mixed operation whereby an open-loop
Picomotor is operated in open-loop mode on one axis and a closed-loop Picomotor is
operated in closed-loop (or open-loop) mode on the other axis.
While operating in closed-loop mode, the Model 8743-CL will respond to motion
command displacements based upon increments of the closed-loop Picomotor positioner's
internal optical encoder, rather than by actual Picomotor steps. The controller will
automatically determine the appropriate number of Picomotor STEPS needed to
accomplish the target COUNTS displacement.
Closed-loop correction takes affect only during position regulation (holding position) as
opposed to while moving. Furthermore, the positioning units must be in 'Counts' (see SN
command) and closed-loop positioning must be enabled (see MM command) for
corrections to occur.
The 8743-CL closed-loop update interval is programmable and can be set from 0.1 second
to about 27 hours. Moreover, for maximum user application flexibility, each axis'
parameter settings are independent and can, therefore, be set to a different interval rate.
NOTE: Closed-Loop correction is automatically disabled after a controller reset,
power-up, or a Following Error condition (see FE command).
NOTE: The user can enable Closed-Loop mode via MM command or by clicking the
Enable Closed-Loop button in the Windows software application.
NOTE: When controlling a standard open-loop Picomotor positioner (1) set 'Units'
option to 'Steps' and (2) disable 'Travel Limit Checking.'

Servo Loop