The tuning of servo systems is a process that can cause
plenty of frustration.
The G320X instructions describe the P, I, and D adjustments,
but there are other factors that can be used to affect
the servo response.
First is the encoder resolution. If you are using the
AMT-102 style encoders, you can set dip switches internal
to the encoder to control the resolution. You should set
only as much resolution as you need. For example you will
want the encoder feedback to offer between 4 and 10 times
as much resolution as the minimum commanded movement that
you need to achieve. Excess resolution can offer tighter
performance, but may also make it more difficult to tune
your system. There is also the possibility that high resolution
settings could require pulses faster than you computer can
Remember that the G320X will use quadrature decoding, so
if your encoder offers 500 pulses per revolution, then
the G320X will be able to see 2000 counts per revolution.
The G320X following error detection circuitry has an
adjustable limit. If your servos struggle to maintain
tight following when moving fast, and you really only
need tight precision when moving slow, then you can
set the DIP switches (number 4 and 5) to allow greater
following error before signaling a fault.
The G320X also has adjustable torque gain. For most
users the default setting works, but sometimes you may
benefit from changing the setting of DIP switches
8, 9, and 10. This will affect the feedback stability.
Lastly, the G320X has a current limit adjustment. If
this is set lower than required by the motor specifications,
it can limit the amount of torque available unnecessarily.
Simulating a fault by removing the fuse is not a valid
approach. The G320X cannot monitor position and provide
fault detection when it does not have power.
The best way to simulate faults is to mechanically
overpower the servo motor so that it is out of position.
You can also connect a momentary switch between the
ERR/RES (terminal 5) and Encoder +5VDC (terminal 7).
This will cause all the G320X drivers that have their
ERR/RES terminals connected together to enter the fault
This simulated fault will cause the G320X drivers to stop
driving the motors, and cause the PMDX-126 to signal an
E-Stop to Mach3. When you then click on the flashing RESET
on the Mach3 screen, the PMDX-126 will reset the G320X
drivers and they will again begin driving the motors.
If you click on the RESET on the MACH3 screen when
the drives have not signaled a fault, the PMDX-126
will NOT disable the drives. This was a design decision
to allow the user to reset Mach without causing the drives
to freewheel if there had not been an E-Stop.
Measuring the voltage to the motors, assuming that
your meter is not confused by the PWM square wave
signal, will tell you how fast the motor should be
trying to turn. It is quite possible to develop full
torque with less that 10 volts applied if the motor is
moving slowly relative to its rated speed. For DC
brush type servo motors, speed will be related to
voltage, and torque will be related to current.
The following error detection circuit and the encoder
are powered by the V+ motor supply voltage on terminal 2,
but should operate correctly at any voltage above 18 volts.
The actual voltage should not influence the error detect
Having a lower motor supply voltage will limit the top
speed of you motor, but my guess is that your supply
voltage is not your problem. Even running at half speed
your motors will probably drive your machine at much
faster speed than you are trying to achieve. Do the
math keeping in mind that motor speed is revolutions
per minute and machine travel speeds are also in inches
per minute. Don't get tripped up inserting a factor of
Hope this give you some ideas without confusing things