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36 Operation Theory
4.1.2 Pulse motion control interface
The second interface of motion and motor control is a pulse train
type. As a trend of digital world, pulse trains represent a new con-
cept to motion control. The counts of pulses show how many steps
of a motor rotates and the frequency of pulses show how fast a
motor runs. The time duration of frequency changes represent the
acceleration rate of a motor. Because of this interface, a servo or
stepper motor can be easier than an analog type for positioning
applications. It means that motion and motor control can be sepa-
rated more easily by this way.
Both of these two interfaces need to provide for gains tuning. For
analog position controllers, the control loops are built inside and
users must tune the gain from the controller. For pulse type posi-
tion controllers, the control loops are built outside on the motor
drivers and users must tune the gains on drivers.
For more than one axes’ operation, motion control seems more
important than motor control. In industrial applications, reliable is a
very important factor. Motor driver vendors make good perfor-
mance products and a motion controller vendors make powerful
and variety motion software. Integrated two products make our
machine go into perfect.
4.1.3 Network motion control interface
Recently, there was a new control interface was introduced--a net-
work motion controller. The command between motor driver and
motion controller is not analog or pulses signal any more. It is a
network packet which contents position information and motor
information. This type of controller is more reliable because it is
digitized and packetized. Because a motion controller must be
real-time, the network must have real-time capacity around a cycle
time below 1 mini-second. This means that non-commercial net-
works cannot do this job. It must have a specific network, such as
Mitsubishi SSCNET. The network may also be built with fiber
optics to increase communication reliability.