Examples and tips
PROGRAMMING MANUAL 239
Revision 3.0
6.1.3 Setting the UNITS axis parameter and gear ratio
In controlling the mechanical axis with the Trajexia TJ1-MC__, a
Servo Driver and a servo motor, the only measurement units that
the hardware understands are encoder counts. All commands to
the driver to move an axis are expressed in encoder counts. All
feedback information about axis positions is also expressed in
encoder counts. When writing programs in BASIC to achieve
movements or a sequence of movements, a user can prefer to work
with user defined units, such as millimeter, centimeter, meter,
degree of angle, "product", "rotation", "stations". The UNITS axis
parameter contains the conversion factor between encoder counts
and user defined units. All axis parameters related to motion and
arguments of axis commands that determine the amount of motion
are expressed in these user units. This parameter enables the user
to define the most convenient units to work with. For example, for a
moving part that makes a linear motion, you can prefer mm, or
fraction of mm. For a moving part that makes a rotation motion, you
can prefer a degree of angle or its fraction. For more information on
the UNITS axis parameter, see section 3.2.270.
However, the user must be aware that not only the UNITS axis
parameter matters in the conversion between encoder counts and
user defined units. Certain Servo Driver parameters and some
characteristics of the mechanical system are also important. The
following sections describe which Servo Driver parameters are
important for this conversion. We also give examples of how to set
those parameters and the UNITS axis parameter, taking the
characteristics of the mechanical system into account.
Conversion between encoder counts and user defined
units
Two very important parameters of the Sigma-II Servo Driver for
conversion of encoder counts into user units are Pn202 and Pn203.
If using a servo motor with an absolute encoder, setting parameter
Pn205 is also necessary.
I52E-EN-03.book Seite 239 Freitag, 29. Juni 2007 11:55 11
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