Rockwell Automation Publication MOTION-RM003I-EN-P - February 2018 381
The Default Motion Resolution value used for scaling factors, Motion Resolution,
Conversion Constant, and Position Unwind, depends on the Motion Unit
selection according to the following table:
Motion Unit Default Motion Resolution
Motor|Load|Feedback Rev 1,000,000
Motor|Load|Feedback mm 10,000
Motor|Load|Feedback Inch 200,000
Motor|Load|Feedback Rev/s 1,000,000
Motor|Load|Feedback m/s 10,000,000
Motor|Load|Feedback Inch/s 200,000
Travel Range Limit
Because the position parameters are sometimes internally limited to signed 32-bit
representation, the Motion Resolution parameter impacts the travel range. In such
a case, the equation for determining the maximum travel range based on Motion
Resolution is as follows:
• Travel Range Limit (in Motion Units) = +/- 2,147,483,647 / Motion
Resolution
Based on a default value of 1,000,000 Motion Counts per Motion Unit, the range
limit is 2,147 Motion Units. When the axis position exceeds this value, the
position accumulators roll-over, essentially flipping the sign of the axis position
value. Motion continuous smoothly through the roll-over but the position values
are obviously not contiguous. This is nominal operation in Unlimited Travel
Mode. While it is relatively rare for this travel range limitation to present a
problem, say in point-to-point positioning applications, it is a simple matter to
lower the Motion Resolution to increase the travel range. The downside of doing
so is that the position data is then passed with lower resolution that could impact
the smoothness of motion. Selecting Limit Travel Mode sets the Motion
Resolution value close to the maximum value that complies with the specified
Travel Range of the application.
Fractional Unwind
In some cases, however, you may also want to specifically configure Motion
Resolution value to handle fractional unwind applications or multi-turn absolute
applications requiring cyclic compensation. In these cases where the Position
Unwind value for a rotary application does not work out to be an integer number
of Motion Counts, the Motion Resolution attribute may be modified to a value
that is integer divisible by the Position Unwind value. This is done automatically
when selecting the Cyclic Travel Mode.
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