3.3 Step response
We will use a step response to determine values for Kp, Ki and Kd. This will be in the
form of starting the turntable from 0 rpm to 33.3 rpm or 33.3 rpm to 45 rpm. The
system is the combination of the Zeus motor controller, your motor, belt, pulley and
platter. To view your system’s step response, use the PIDTuning application, connect
the serial port and click the Start button. Use this graph panel will plot the transient
response of your system. Typically, the transient response is measured by first
commanding a step, then measuring how quickly a system takes to reach a steady
state. Using the transient response, you can calculate the maximum overshoot, rise
time, peak time, and settling time of your system.
3.4 Stability in the time domain
Use Step Response to determine the relative stability of the system. A system is
considered stable if the actual value is finite when the commanded value is finite. In
other words, a system is stable if a commanded position results in the motor coming
to the desired speed.
A system is considered unstable when any commanded value typically results in an
exponential increase in rotational speed error. In other words, a system is unstable
when its attempts to achieve a set value that results in oscillations that never dampen.
The following graphs are for illustration of general PID tuning theory – they are not
from the PIDTuning application. The PIDTuning application will produce similar
results but the graphs will not be quite as smooth.
The following figure, illustrates a Step Response and shows a typical step response
for a motor. Following the chart is a description of elements to consider when
determining the stability of a PID control system.
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General