Danaher Motion
06/2005
Project
M-SS-005-03 Rev
E
69
The MC provides the external position through the axis property,
POSITIONEXTERNAL
or
PEXT
. This variable contains the accumulated
encoder movement of the drive’s external encoder input. It is updated every
SERCOS cycle.
You can access
PEXT
two ways: realtime or on a as-needed basis. To
access
PEXT
on an as-needed based, issue
IDNVALUE
. For example:
Dim Shared StorePExt as Double
StorePExt = IDNValue(1, 53, 7)
This gets
PEXT
in counts, not user units. You can access
PEXT
in realtime
by properly configuring the telegram for the axis with the external encoder.
The SERVO
STAR
MC allows you to control the units of the
POSITIONEXTERNAL
(
PEXT
). This is controlled with
<axis>
.
POSITIONEXTERNALFACTOR
or
<axis>
.
PEXTFAC
. The process
is identical to setting position units for an encoder. The external position and
velocity factors are only effective for cases when the SERCOS telegram is
configured to transmit the external encoder.
Do not access
PEXT
using
IDNVALUE
because the encoder values coming
into the drive are subject to rollover. The MC continuously monitors these
values and adjusts the value when a rollover is detected. The values
accessed via the SERCOS service channel cannot be monitored for rollover.
Also, external position units are not in effect.
The MC provides the external velocity through the
<axis>.VELOCITYEXTERNAL
or
<axis>.VEXT
. This variable contains the
accumulated encoder movement per millisecond and is also updated every
SERCOS cycle when the SERCOS telegram is configured to transmit the
external encoder.
The MC allows you to control the units of
VELOCITYEXTERNAL
with
<axis>.VELOCITYEXTERNALFACTOR
or
<axis>.VEXTFAC
. The process
is identical to setting position units except that
<axis>.VEXTFAC
can only be
input as an encoder signal.
3. 9
L
IMITS
This section outlines the many types of limits you can impose on the MC
system. These limits help protect the machine from excessive excursions of
travel, speed, and torque. There are three types of limits in the SERVO
STAR
system:
MC Generator Limits
MC Realtime Limits
Drive Limits
Limits can be imposed in several ways. First, some limits are imposed by the
MC and others by the SERVO
STAR
drive. Limits can be checked in realtime
or they can be checked only for subsequent actions.
MC Generator
limits affect subsequent commands to the motion generator.
For example, if you change an acceleration limit, this has no effect on the
current motion command, but it applies to subsequent motion commands. If
the axis is not in a jog or acting as a slave, then
POSITIONMIN
and
POSITIONMAX
(position limits) are checked only at the beginning of the
move.