Newport ESP300 Series, Руководство пользователя, Страница: 263 / 314

Disadvantages
Some of the DC motor's disadvantages are:
•
Requires a position feedback encoder and servo loop controller
•
Requires servo loop tuning
•
Commutator may wear out in time
•
Not suitable for high vacuum application due to the commutator
arcing
•
Hardware and setup are more costly than for an open loop stepper
motor (full stepping)
5.7 Drivers
Motor divers must not be overlooked when judging a motion control
system. They represent an important part of the loop that in many
cases could increase or reduce the overall performance.
The ESP300 is an integrated controller and driver. The controller part
is common for any configuration but the driver section must have the
correct hardware for each motor driven. The driver hardware is one
driver card per axis that installs easily in the rear of the controller.
Each card has an end-plate with the 25 pin D-Sub motor connector
and an identifying label. Always make sure that the motor specified
on the driver card label matches the label on the motion device.
There are important advantages to having an integrated
controller/driver. Besides reducing space and cost, integration also
offers tighter coordination between the two units so that the controller
can more easily monitor and control the driver's operation.
Driver types and techniques vary widely. In the following paragraphs,
we will discuss only those implemented in the ESP300.
5.7.1 Stepper Motor Drivers
Driving a stepper motor may look simple at first place. For a motor
with four phases, the most widely used type, the user will need only
four switches (transistors) controlled directly by a CPU (
Figure 5.44 ).
This driver works fine for simple, low performance applications. But,
if high speeds are required, having to switch the current fast in
inductive loads becomes a problem. When voltage is applied to a
winding, the current (and thus the torque) approaches its normal value
exponentially (
Figure 5.45 ).
Section 5 – Motion Control Tutorial 5-33