Newport MM4005, Руководство пользователя

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EDH0162En1040 – 06/99
MM4005 Motion Control Tutorial
keep in mind are:
• For a constant load, the velocity is approximately proportional to the
voltage applied to the motor.
• For accurate positioning, DC motors need a position feed-back device.
• Constant current generates approximately constant torque.
• If DC motors are turned externally (manually, etc.) they act as genera-
tors.
4.6.2.1 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.
4.6.2.2 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).
Drivers
Motor drivers must not be overlooked when judging a motion control sys-
tem. They represent an important part of the loop that in many cases could
increase or reduce the overall performance.
The MM4005 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 match-
es 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 coordina-
tion 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 MM4005.
4.7.1 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 (Fig. 4.44).
4.7
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