Axis Type: Rotary and Linear

This topic describes rotary and linear axes. All axes are by default linear. To define an axis as rotary, use the Linear/Rotary axis parameter.

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 descriptions of all available RMC axis types, see the Axis Types Overview topic. 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.