Geo Brick Drive User Manual
Motor Setup
164
Dominant Clock Settings
The choice of clock settings usually relies on the system requirements, and type of application.
Minimum PWM Frequency
The minimum PWM frequency of a system is based on the time constant of the motor. In general, the
lower the time constant, the higher the PWM frequency should be. The motor time constant is calculated
dividing the motor inductance by the resistance (phase-phase). The minimum PWM Frequency is then
determined using the following relationship:
;
=>
Example:
A motor with an inductance of 6.1 millihenries (mH), and a resistance of 11.50 Ohms (
phase-phase) yields a time constant of 0.53 milliseconds. Therefore, the minimum PWM Frequency is
about ~6000Hz (6.0 KHz).
Note
Systems with very low time constants (needing higher PWM
frequencies) may require the addition of chokes or in-line inductive
loads to obtain a good current loop bandwidth.
Recommended clock Frequencies
The default clock settings in the Geo Brick Drive should work fine for the majority of applications, they
are set as follows:
Phase Clock:
9.000 KHz
PWM Clock:
4.500 KHz
Servo Clock:
2.258 KHz
The need to change clock rates depends on specific requirements and motor/encoder hardware:
Phase Clock:
The phase clock is directly related to the current loop calculation and
current sensor
reads. Typically, the phase clock is set to twice the PWM frequency. Setting it faster is
meaningless and will not result in any performance enhancement.
PWM Clock:
The PWM clock is directly related to the inductance and resistance of the motor. It can be
calculated empirically as shown in the aforementioned equation.
Servo Clock:
The Servo clock is directly related to motor calculation and servo (encoder read, motor
command write) update rate. Higher servo frequencies result, in general, in improved
performance. The need for boosting the servo clock could come from several factors,
such as high speed/precision applications, synchronizing to external events, position
capture/compare at high rates, kinematics calculation. Hardware such as high resolution
encoders (e.g. serial, sinusoidal), linear motors, and galvanometers are usually set up with
higher servo rates for best results.
Содержание Geo Brick
Страница 5: ...4...
Страница 286: ...Geo Brick Drive User Manual Appendix A 286 APPENDIX A Schematic Samples Watchdog X15 Inputs J6 J7...
Страница 287: ...Geo Brick Drive User Manual Appendix A 287 Outputs J6 J7 603793 109 and earlier Outputs J6 J7 603793 10A and later...
Страница 288: ...Geo Brick Drive User Manual Appendix A 288 Limits Flags J4...
