Accessory 24E2S
Motor Parameter Setup for UMAC and MACRO
25
MOTOR PARAMETER SETUP FOR UMAC AND MACRO
The motor parameter setup is identical for both the Turbo PMAC and the Ultralite/MACRO Station
systems. The key motor parameters to setup are the maximum pulse frequency output and the PID gains.
Ix69 is the motor x output command limit for motor number x. For stepper motor systems, this parameter
defines the magnitude of the largest number that may be placed into the PFM register for output pulse
frequency. If the PMAC2 calculates a larger number than Ix69’s value, the number will be clipped to the
limiting value and the result of a limited output value will be a larger following error.
The default value appears to exceed most requirements for stepper motor applications, but the maximum
pulse rate should be limited near the end of the setup process.
The formula for setting Ix69 is:
65536
x
MHz
,
KHz
(
PFMClock
)
MHz
,
KHz
(
cy
MasFrequen
69
Ix
The default setting for Ix69 is 20480 and the default PFM clock setting is set to approximately 9.8304
MHz. Using the default values and solving for Max Frequency, a maximum frequency output would be
3.0719 MHz. Putting a cap on the pulse output rate may keep the stepper system from exceeding its
maximum step rate, which will help keep the motor from losing sync with the PMAC2.
PMAC2 Motor Servo Gain I-Variables for Stepper Motors
The PMAC2 applies its gain formulas for stepper motor systems the same way it does for a classic servo
system. The basic difference with a stepper system is that the typical encoder feedback interface is
handled using electronic circuitry rather than a physical encoder.
The PMAC2 Stepper interface allows the use of both an electronic encoder feedback and/or physical
encoder feedback (depending upon the hardware settings). When used with an actual physical encoder,
the axis should be tuned as if it were a typical servo motor.
The process of tuning the simulated feedback loop is identical to tuning a servo motor except that some of
the parameters become more predictable:
Ix30 Motor x Proportional Gain
To create a closed loop position response with a natural frequency of approximately 25Hz and a damping
ratio of 1, use the following calculation:
)
MHz
(
xPFMClock
08
Ix
660000
30
Ix
Example
: PFMCLK is set to default of 9.83 MHz, and Ix08 is set to default of 96.
Ix30 = 660,000 / (96 * 9.83) = 700.
Ix31 Motor x Derivative Gain
Derivative Gain is set to 0 because the motor system behaves like a velocity-loop servo drive. This
parameter sets the system damping which should be unnecessary.
Ix32 Motor x Velocity Feedforward Gain
Use the following equation to establish a value for Ix32:
)
kHz
(
xServoFreq
6660
32
Ix
ServoFreq (kHz) is the frequency of the servo interrupt as established by I900, I901, and I902.
Example
: ServoFreq is set to default of 2.258 kHz (I900 = 6527, I901 = 0, I902 = 3).
Ix32 = 6660
2.258
15,050.
