Installation guide

248 Servo Drive
Step 1: Measure
The system gain is a measure of the overall responsive-
ness of the system. Higher inertia and/or lower torque
yields lower system gain. Lower inertia and/or higher
torque yields higher system gain. The system gain
number is used when the software calculates the servo
gains. A lower system gain requires higher calculated
controller gains in order for the motor to track a given
profile response.
Clicking
Measure System Gain
instructs the controller
to provide a “bump” of torque to the motor. Three pa-
rameters,
Output, Speed
, and
Distance Limit
are used
to measure system gain.
The
Output
text box is used to select the amount of
voltage that the controller will use to bump the motor.
The range of the Output is 0 to 10 volts where 10 volts
represents peak torque. Typically the default parameter
of 2 volts is adequate, although some large inertia sys-
tems may require the Output be set to 3 or 4 volts.
The
Speed
text box is used to select the target velocity
for the gain measurement. During gain measurement,
the output torque will be applied to the motor until the
speed set here is reached. The default speed is usually
sufficient if revs/sec is used for the unit of measure.
The value in the
Distance Limit
text box limits the
distance that the motor will turn during the gain meas-
urement. If the
distance limit
is reached before the
motor reaches the
speed
indicated, or if the speed can-
not be reached with the voltage entered, an error mes-
sage will appear. If an error appears, try increasing the
distance limit or raising the voltage output slightly.
Generally, the default parameters for these three pa-
rameters should be used during the gain measurement,
provided that the unit per motor rev was left at the de-
fault of 1.
Caution!
When the
Measure System Gain
button is clicked, the motor will move quickly
and abruptly for a short distance
.
If the gain measurement is unsuccessful, verify that the
motor moves properly with a constant torque command
applied. Clicking the Apply Voltage button on the tun-
ing screen will do this. Clicking the
Apply Voltage
button will output a constant torque to the motor pro-
portional to the command voltage. Start with zero and
click on the up or down arrows to apply positive or
negative torque respectively. Unless the system has
high friction, the motor should begin to move with less
than one volt applied. Check that the motor torque is
smooth and continuous in both directions by applying
small amounts of positive and negative voltage.
Step 2: Calculation
The system bandwidth is essentially the maximum fre-
quency of excitation to which the system will respond.
Generally, higher bandwidth systems are “stiffer” or
“tighter”. Lower bandwidth systems are “soft” or
“sluggish”. Generally bandwidths range between 10 to
60 Hz (cycles per second). The auto tuning procedure
uses the bandwidth setting along with the measured
system gain to calculate the appropriate servo gains for
the system. The default bandwidth of 30 Hz is usually a
good starting point, although sometimes the bandwidth
must be lowered to achieve a stable system, or raised to
achieve a fast enough response.
Calculate Servo Gains
Clicking the
Calculate Servo Gains
button will use the
bandwidth and measured system gain to calculate the
Kp, Ki, Kd, Intlim (and Kaff if applicable) parameters.
These fields will be updated after the calculation is
complete.
Step 3: Update
Clicking Update Gains will update the gains to the
controller immediately.
Caution! Updating the gains
may change the dynamics of the system such that it
becomes unstable and oscillatory.
If a loud buzzing
or vibration occurs after updating gains, the
Shutdown
button should be clicked. It is also possible that a fault
will occur if the oscillation overtaxes the servo drive. In
this case you will have to enter the terminal screen and
clear the error by typing ERR or ERRM. If necessary,
go to
Step 2
and
lower the bandwidth
and re-calculate
the servo gains. Now update the gains again. Repeat
this process until the system is stable and will smoothly
resist loading in both directions.
Step 4: Response
Step 4 allows test motion profile parameters to be en-
tered so that the proper motion response may be veri-
fied.
Accel, Decel, Speed
and
Move Distance
parame-
ters describe the move that the motor will try to follow
during the test. The
display time
is adjustable so that
shorter or longer moves may be fully displayed. The
unit for each parameter is configured in the System
Folder.
Once the profile parameters setup is complete, the sys-
tem is ready to attempt to execute the move. Clicking
the
Execute move
command button will command the
motor to execute the move profile. The controller will
log the response of the motor and display the results on
the screen graphically. The position error, torque com-
mand, encoder velocity, etc. may be viewed by clicking
on the drop down list at the top of the window. The
displayed graph of the position error is the error based
on quadrature signal feedback from the encoder (for ex-
ample there are 4000 counts or pulses per revolution on
a 1000 line encoder).The response
may be observed to
verify proper performance for the programmed profile.
If the response is
acceptable, Quit the servo screen and
Save the configuration. You will now have to Compile
and Download the project for the new servo informa-
tion to permanently take effect.