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31
10 Controller Adjustment
When any actuator made by
Newport Corporation
is connected to the
NPCxxxDIG
, amplifier their specific
values are read from the actuator’s ID-chip. The Digital Signal Processor (DSP) of the amplifier is set with
these values. These parameters were investigated in the
Newport Corporation
laboratory and ensure safe
function of the actuator.
There are no kp-, ki-, and kd-values for actuators without a measurement system because the closed loop
mode is impossible in this configuration. Closed loop is automatically switched off.
To adapt the controller properties to your special application please start with the default values. At
first please switch on the closed loop mode by pressing the
encoder knob “OFFSET” or by the
command
cl,1
via RS232. Change one parameter step by step and check the result with the
oscilloscope on the ANALOG 9pin SUB-D socket of the amplifier. You must install a monitoring
output to
position value in open loop
with the command
monsrc,6
.
In general, change the parameters in small steps and, depending on the actuator's reaction, slightly increase
the step width. If the system begins to oscillate, switch off the closed loop immediately by pressing the
encoder knob, then reset the last values entered!
First of all, check the function of the notch filter. This has been factory adjusted so that the main resonant
frequency is suppressed in an actuator with standard mass loading. If your application has a different mass,
the resonant frequency changes (higher mass = lower frequency).
The notch parameters are adjustable
with the commands
notchon
,
notchf
and
notchb
.
The sweep function of the internal function generator can be used to determine the resonant frequency. Use
function generator
in the
menu
of the actuator. Set the amplitude to 5%, the offset to 0%, and the sweep
time to 1 (1sec/decade). Set the amplifier to open loop (“OL/CL” LED lights green). With the MOD/MON
cable (MON plug) you can connect the oscilloscope to the ANALOG socket of the amplifier. The following
adjustments on the oscilloscope are required: store function, time base = 0.5 sec/div and input voltage =
0.1V/div. The display shows the response of the actuator measured by the integrated measurement system.
Before the measured curve swings out, there is a position where the amplitude is 0 Volts. This is the adjusted
notch frequency. At the resonant frequency, the measured curve goes very high. At this point you have to
adjust the notch frequency to the resonant frequency to linearize the curve. Using the notch filter might
increase noise.
The correct ki-value is determined as follows:
In the
function generator
menu,
set rectangle to 1 Hz, amplitude to about 50%, and offset to 25%. Please set
the monitoring output to
Umes/CL
in the
analog i/o
menu. The following adjustments on the oscilloscope
are
required:
store
function,
time
base
=
0.05sec/div
and
input
voltage = 1V/div. Set the amplifier to closed loop (“OL/CL” LED lights yellow). The oscilloscope display
shows the step response of the actuator measured by the integrated measurement system. If the slew rate is
too low, please increase the ki-value in the
digital controller
menu. The over swing after the rise time
should be smaller than 1% of the total step.
In these adjustments, the actuator system can begin to oscillate in resonant frequency. Please switch
off the closed loop immediately by pressing the encoder knob “OFFSET”. Then reset the last values
entered! Continuous use at resonance can damage the actuator!
Now you can try to increase the slew rate in
slew rate/filter
menu
,
as long as no oscillation or large over
swing occurs.
Summary of Contents for NPC DIG Series
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