Drivers; Stepper Motor Drivers - Newport ESP6000 User Manual

Advantages
DC motors are preferred in many applications for the following reasons:
• smooth, ripple-free motion at any speed
• high torque per volume
• no risk of loosing position (in a closed loop)
• higher power efficiency than stepper motors
• no current requirement at stop
• higher speeds can be obtained than with other types of motors
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)
6.7

Drivers

Motor drivers 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 ESP system is an integrated controller and driver. 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 varying widely, in the following paragraphs we
will discuss only those implemented in the ESP system.

6.7.1 Stepper Motor Drivers

Driving a stepper motor may look simple at first glance. For a motor with
four phases, the most widely used type, we need only four switches (tran-
sistors) controlled directly by a CPU (Figure 6.7-1).
6 - 2 8
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com