Juno Step Motor Control IC User Guide
55
9
9.Current Loop
In This Chapter
Settable Parameters
Signal Processing
Figure 9-1:
Current Loop
Control Flow
Diagram
provides a summary of the control flow of Juno’s current loop control module when driving a step motor.
Current control is a technique used for controlling the current (and therefore the torque) through each winding of the
motor. By precisely controlling the current, response times improve, motor efficiency is higher, motion smoothness
increases, and top speed increases.
The Juno digital current loop utilizes the desired current along with the measured current for each motor winding to
perform a current loop function and generate an output voltage command for each motor coil. The output command
for each coil is then passed to the motor output module which generates the precise PWM (pulse width modulation)
timing output signals to control external switching circuitry.
To control the current loop three parameters are specified for both a “D” loop and a “Q” loop by the user; Kp, Ki, and
Ilimit. Two of these are gain factors for the PI (proportional, integral) controller, one is a limit for the integral
contribution. Determining correct Kp, Ki, and Ilimit parameters for the current loop controller gains can be done in a
number of ways but the easiest is to utilize the auto-tuning facility provided within PMD Corp.’s Pro-Motion software
package.
By default the current loop module is disabled. To enable the current loop the user must enable the corresponding flag
of the Operating Mode register.
To activate current loop processing the current loop flag of the Operating Mode register must be enabled.
_
+
P
I
+
+
To Motor
Output
Module
CurrentA-D
Actual
Current
Current
Error
x
.5
x
.625
Phase A & Phase B
Command
From Microstep
Waveform
Generator
