Motion Control Primer
MultiFlex PCI 1000 Series User's Manual
21
Open loop with position verification
By adding a feedback device (like an encoder) to a traditional open loop stepper you would have what is
known as an open loop with position verification system. For some applications where the higher costs,
complexity, or torque limitations of closed loop servos may be prohibitive a stepper coupled with an
encoder makes for a perfect compromise.
Contrary to many servo applications, where the following error of the axis along the entire path is of great
concern to the machine designer, for many stepper applications the user is only concerned about the 'end
of move' final position of the axis. By adding an encoder (typically directly coupled to the stepper motor
shaft) the user can monitor the 'end of move' final position of the axis and issue 'correction moves' to
compensate for any possible lost steps. For additional information on open loop with position verification
systems please refer to page 143.
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