Delta RMC151 - Manual (Page 90)

RMC70/150 and RMCTools User Manual
A rotary axis is typically used for rotary feedback devices such as encoders. The RMC
supports rotary feedback for both control axes and reference axes. For rotary axes, the counts
per revolution must be a power of two, such as 1024, 8192, etc. This typically means the
encoder counter per turn must be a power of two.
For details and examples on using rotary motion, see the Using Rotary Motion topic.
A linear axis is the standard axis type with a transducer that has definite endpoints, for
example a magnetostrictive rod.
Rotary vs Linear
SSI, Quadrature, and Resolver position inputs can be configured to be rotary. All other
input types are linear only. The following items point out the differences between these
rotary and linear orientations for position inputs:
• 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.
Similarly, the target is also kept within this range. Any control being performed using
this input is not interrupted; this is not seen as a position discontinuity.
• The position units for a linear input never wrap.
• Rotary inputs use the Position Unwind parameters to determine how many counts can
be accumulated before wrapping. This is used in conjunction with the Position Offset
parameter, to define the position unit range. Linear inputs do not use the Position
Unwind parameter at all.
• Linear incremental inputs do not use the Position Offset parameter because the actual
position is really an accumulator, so offsetting the position is done instead by resetting
the accumulator through homing or commands. Linear absolute inputs use this
parameter to offset the position when converting from counts to position units. Rotary
inputs (incremental or absolute) use this parameter to adjust the modulo position
range up or down. For example, the position units on a rotary input with modulo 2000
could be shifted to range from -1000 to +1000 or from 0 to 2000.
• Linear position inputs use the Positive and Negative Travel Limits to restrict the target
position. Rotary position inputs do not use these parameters.
3.3.4.2. Axis Type: Incremental and Absolute
This topic describes incremental and absolute axes. The feedback type of most axes
determines whether it is incremental or absolute. Only position axes with SSI or Resolver
feedback can be either.
Absolute Axes
An absolute axis has a feedback type that provides absolute information. That is, it
always knows its exact position. When the RMC powers up, the position is known. For
example, the voltage or current from an analog input will always tell exactly where the
axis is located.
Incremental Axes
An incremental axis has a feedback type that provides only information about how much
it has incremented. When the RMC powers up, it has no information about where the axis
is, but it can keep track of how much the position changes. Incremental axes typically
need to be homed so the position is known.
Quadrature inputs are always incremental.
By Axes Type
The following feedback types are always absolute:
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