Motion Control
Precision MicroControl Corp.
80
Closed Loop Steppers
The advancements in stepper motor/micro stepping driver technology have allowed many machine
builders to maintain ‘servo like’ performance while reducing costs by moving to closed loop stepper
systems. While closed loop steppers will still be susceptible to ‘stalling’, they are not plagued with the
familiar open loop stepper system problem of loosing steps due to friction (mechanical binding) or system
resonance.
For high accuracy stepper applications, the controller supports closed loop control of stepper motors
using quadrature incremental encoders for position feedback. The stepper axis will be controlled as if it is
a closed loop servo, the quantity and frequency of step pulses applied to the stepper driver is based on
the trajectory parameters of the move and the position error of the axis. Prior to attempting to operate a
stepper motor in closed loop mode the basic system components (motor, driver, wiring, and controller)
should be verified by moving in open loop mode. For information on operating an open loop stepper
please refer to the
Stepper Basics
and
Moving Motors with Motor Mover
sections in this chapter. If the
stepper motor does not operate as expected please refer the
Troubleshooting
chapter.
i
While executing closed loop stepper motion, when the target position
equals the current encoder position, the step pulse generator (PID filter)
will be turned off within 1 micro second.
Unlike a closed loop servo, if the final position of the stepper encoder is
beyond the target position of the move
the motor will not be
commanded to move back to the target
.
Closed Loop Stepper Setup
There are four steps required to configure a stepper to operate in closed loop :
1) Connect and verify operation of the encoder
2) Define the Encoder / Steps ratio
3) Set the trajectory parameters
4) Tune the axis
Connect and verify the encoder
Connect the stepper motor's encoder to the controller per the connector pinouts described in chapters 5
and 10 of this manual.
To verify the operation of the encoder open the Motor Mover program (Start\Programs\Motion
Control\Motion Integrator\Motor Mover). From the Setup dialog select Closed Loop Mode and OK.:
Figure 30. Select Setup to open the dialog
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