Delta RMC151 - Manual (Page 40)

RMC70/150 and RMCTools User Manual
3. The Position Scale is equal to the number of position units per count, for example,
using inches and a resolution of 0.005 mm:
4. If you wish to reverse the direction of the feedback, make the Scale negative.
5. Download the Scale to the RMC.
6. Calculate the Position Offset:
• Look at the Actual Position register and the Counts register.
• Move the axis to a point where you know what you want the position to be
(such as 0). Called this the Desired Position. Look at the Actual Position
register. Call this position P
0
.
• Calculate the Position Offset using the following equation:
Position Offset = Desired Position - P
0
.
6. Download the Offset
2.2.8. Rotary Scaling
SSI, resolver, and quadrature axes can be configured as rotary axes. To have any useful
meaning, the counts from the encoder must be scaled to position units. This topic describes
the scaling parameters for a rotary axis and provides instructions on how to scale the axis.
Delta Recommends using the Scale/Offset Wizard for scaling the position. If you need to do it
manually, read this topic.
Calculating the Scale Parameters
To calculate the scale parameters, use the Rotational Scale/Offset wizard.
You can also enter the scale parameter manually. Refer to the Scaling Parameter
Details section below for a description of each parameter.
Scaling Parameter Details
A rotary axis uses the Count Unwind, Position Unwind, Position Offset, and Count Offset
parameters to calculate the position units from the counts:
• Count Unwind
The counts for a rotary input are kept within a defined range. When the input goes
beyond one end of this range, the counts wrap to the other end of the range. The Count
Unwind parameter defines this range. Any control being performed using this input is
not interrupted; this is not seen as a position discontinuity.
For absolute rotary axes, this parameter must be a power of 2. If it were not, the wrap
point of the counts would not coincide with the wrap point of the encoder and it would
not be possible to determine absolute position.
RMC Resolver axes will always give 65,536 counts per revolution.
Example:
Consider a single-turn SSI encoder with 8192 counts per revolution. If the Count
Unwind is set to 8192, the counts will go from 0 to 8191 and wrap once per revolution.
If the Count Unwind is set to 2048, the counts will go from 0 to 2048 and will wrap four
times per revolution.
• Position Unwind and Position Offset
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