Newport MM4006, User Manual

Page: 324 / 411

MM4006 M o t i o n Control Tutorial
The best approach is to carefully study the application, extract from the
specification sheet the applicable discrete error parameters and combine
them (usually add them) to get the worst-case general error applicable to
the specific case. This method not only offers a more accurate value but
also gives a better understanding of the motion control system perfor-
mance and helps pinpoint problems.
Also, due to the integrated nature of the MM4006 system, many basic
errors can be significantly corrected by an other component of the loop.
Backlash, Accuracy and Velocity Regulation are just a few examples where
the controller can improve motion device performance.
4.3
Control Loops
r
When talking about motion control systems, one of the most important
questions is the type of servo loop implemented. The first major distinction
is between open and closed loops. Of course, this is of particular interest
when driving stepper motors. As far as the DC servo loops, the PID type is
by far the most widely used.
The MM4006 implements a PID servo loop with velocity feed-forward for
both DC and stepper-motor motion devices. It is not just a static closed
loop, when the motion is stopped, but a fully dynamic one.
The basic diagram of a servo loop is shown in Fig. 4.13. Besides the com-
mand interpreter, the main two parts of a motion controller are the trajec-
tory generator and the servo controller. The first generates the desired
trajectory and the second one controls the motor to follow it as closely as
possible.
Command
Interpreter
-
Trajectory Trajectory
Generator
Motion Controller
Servo
Controller Controller
Encoder
Fig. 4.13 — Servo Loop.
N e V V p O r t . 4 . 1 3 E D I 101glEn1020 — 03/03