Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 279)

Publication 1784-UM003A-EN-P – June 2003
Motion Object Attributes 271
Motion Status Attributes The Motion Status Attributes associated with the Axis Object provide access
to the current and historical position velocity, and acceleration information of
the axis. These values may be used as part of the user program to implement
sophisticated real time computations associated with motion control
applications. A list of all Motion Status Attributes is shown in the tables below.
For all of the Motion Status attributes to return a meaningful value, the
‘Conversion Constant’ Axis Configuration Attribute must be established.
Furthermore, attributes having velocity units (Position Units / Sec) must also
have a valid coarse update period which is established through association with
a fully configured Motion Group Object.
All Motion Status attributes support Direct Tag Access via RSLogix5000
software. Thus, a Motion Status attribute may be directly referenced in a
program as .. An example of this
might be FeedAxis.ActualPosition.
To avoid the unnecessary processor effort associated with real-time conversion
of certain Motion Status tags that are not of interest to the user, it is necessary
to explicitly activate real-time update of these attributes via the Auto Tag
Update attribute of the associated motion group. A subset of the Motion
Status attributes must have the Auto Tag Update attribute enabled or the tag
value will be forced to zero. The following Motion Status attributes are
affected:
• Actual Position
• Actual Velocity
• Actual Acceleration
• Master Offset
• Command Position
• Command Velocity
• Command Acceleration
• Average Velocity.
Actual Position Actual Position is the current absolute position of an axis, in the configured
Position Units of that axis, as read from the feedback transducer. Note,
however, that this value is based on data reported to the ControlLogix
Processor as part of an ongoing synchronous data transfer process which
results in a delay of one coarse update period. Thus, the Actual Position value
that is obtained is the actual position of the axis one coarse update period ago.
GSV/SSV Access Attribute Name Data Type Values
GSV Actual Position REAL Position Units