84
APEX615n Installation Guide
Step 4
Set the Maximum Position Error (SMPER):
The SMPER command allows you to set the maximum position error allowed before an error
condition occurs. The position error, monitored once per system update period, is the
difference between the commanded position and the actual position as read by the feedback
device selected with the last SFB command. Larger values allow greater oscillations/motion
when unstable; therefore, smaller
SMPER
values are safer.
When the position error exceeds the value entered by the SMPER command, an error condition
is latched (see TAS or AS bit #23) and the 6000 controller issues a shutdown to the faulted
axis and sets its analog output command to zero volts. To enable the system again, the
appropriate DRIVE1 command must be issued, which also sets the commanded position equal
to the actual feedback device position (incremental devices will be zeroed).
If the SMPER value is set to zero, the position error condition is not monitored, allowing the
position error to accumulate without causing a fault.
Step 5
Optimize the Proportional (SGP) and Velocity (SGV) gains (
see illustration
for tuning process
):
a. Enter the following commands to create a step input profile (use a comma in the first
data field when tuning axis 2—e.g., D,1ØØ):
Command Description
> A999 Set acceleration to 999 units/sec
2
> AD999 Set deceleration to 999 units/sec
2
> V3Ø Set velocity to 30 units/sec
> D1ØØ Set distance to 100 units
b. Start with an SGP command value of 0.5 (SGPØ.5 or SGP,Ø.5).
c. Enter the GO1 or GO,1 command depending on which axis is being tuned at the time.
d. Observe the plot of the commanded position versus the actual position on the
oscilloscope. If the response is already very oscillatory, lower the gain (SGP); if it is
sluggish (overdamped), increase the SGP gain.
Repeat Steps 4.c. and 4.d. until the response is slightly under-damped.
e. Start with an SGV command value of 0.1 (SGVØ.1 or SGV,Ø.1).
f. As you did in Step 4.c., enter GO1 or GO,1.
g. Observe the plot on the oscilloscope. If the response is sluggish (overdamped), reduce
the SGV gain. Repeat Steps 4.f. and 4.g. until the response is slightly under-damped.
☞
Refer to the
Tuning
Scenario
section
later in this chapter
for a case example.
h. The flow diagram below shows you how to get the values of the proportional and
velocity feedback gains for the fastest, well-damped response in a step-by-step fashion.
The tuning principle here is based on these four characteristics:
• Increasing the proportional gain (SGP) can speed up the response time and increase
the damping.
• Increasing the velocity feedback gain (SGV) can increase the damping more so than
the proportional gain can, but also may slow down the response time.
• When the SGP gain is too high, it can cause instability.
• When the SGV gain is too high, it can cause the motor (or valve, hydraulic
cylinder, etc.) to chatter.
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