To achieve the highest performance, the stepper motor can be treated as a 2 phase brushless servo motor. Current to the motor will then be controlled as a function of the error signal just as with standard servo motors. Galil refers to as 2 Phase Brushless mode, or 2PB. Figure 7 details the stepper motor system being driven in this mode. Now, rather than step pulses, a torque command signal (brown line) is generated by the controller to be fed to one of Galil's internal amplifiers operating in 2PB mode in order to control the position of the motor. times. A stepper motor driven in 2PB mode is analogous to a classic servo motor attached to a speed reduction gearbox.
Closed Loop Stepper Control
By leveraging Galil's methods of closed loop stepper control, the various shortcomings of stepper motors can be overcome. The endpoint position can be adjusted for inaccuracies with stepper position maintenance mode, the position can be dynamically adjusted with closed loop microstepping, and lastly the stepper motor can be treated as a 2-phase brushless servo to further increase the performance and efficiency of the motor. If you have questions on which mode of closed loop stepper operation is appropriate for your application, contact our Applications Engineering department at oyostepper.com.
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