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 SERVOSTAR 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 LIMITS
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 SERVOSTAR
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 SERVOSTAR 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.
