Delta RMC151 - Manual (Page 917)

9 Register Reference
Type: Axis Parameter Register
RMC70 Address: %MDn.11, where n = 12 + the axis number
RMC150 Address: %MDn.11, where n = 24 + the axis number
System Tag: _Axis[n].CntOffset, where n is the axis number
How to Find: Axes Parameters Pane, Setup tab: Primary Control Setup
Data Type: DINT
Units: pu
Range: any
Default Value: 0
Description
This parameter is used on SSI and Resolver position axes with absolute positions. The
Count Offset offsets the transducer Counts before the Counts are converted to position
units. This parameter has no effect if the axis is set to incremental.
The Count Offset fits in the conversion of counts to an actual position as follows:
Rotary Axes:
Actual Position [pu] = ((Counts [cnt] + Count Offset [cnt]) x Position Unwind [pu]
/ Count Unwind [pu/cnt] ) + Position Offset [pu]
Linear Axes:
Actual Position [pu] = ((Counts [cnt] + Count Offset [cnt]) x Position Scale
[pu/cnt]) + Position Offset [pu]
The Count Offset is typically used in the following situations:
• On rotary axes with absolute encoders, to set the zero point of the axis.
• On linear axes that use an absolute encoder, the Count Offset is needed to insure
that the total counts (Counts + Count Offset) never cross the roll-over point
(below zero or above max count).
Example: Rotary Axis with Rotary Absolute Encoder
Consider an SSI rotary absolute encoder with 8192 counts per revolution, with the Count
Unwind to 8192, and the Position Unwind to 360. Therefore, the positions will go from 0
up to, but not including, 360. You want the zero point (zero counts) to be at the top of
the rotation so it will read 0 degrees, but perhaps the way the transducer is mounted
gives you 1000 counts at the top. You can set the Count Offset to -1000, which will give
you zero counts at the top, and therefore, 0 degrees.
Example: Linear Axis with Rotary Absolute Encoder
Consider a rack and pinion system with 10000 mm of travel and an encoder mounted on
the pinion. 1 turn on the encoder will move 100 mm. The entire travel will therefore span
100 turns. The encoder is an SSI multi-turn rotary absolute encoder with 4096 counts per
revolution and 4096 turns.
The maximum counts is 16,777,216.
The entire span of counts over the travel range will be 100 turns x 4096 counts =
409,600 counts.
The Position Scale is 100 mm / 4096 counts = 0.024414 mm/cnt
When setting up the axis, the user started with the pinion all the way to the negative end
of the travel. At that point, the encoder counts happened to be 16,561,242. Moving to the
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