Virtual Axes

Virtual axes have no feedback or output. The RMC can have any number of virtual axes as long as the total number of axes for that controller type is not exceeded, as listed in Axis Types Overview.

Virtual axes have a Target and Command Position, but no Actual Position. Motion commands issued to the axis will move the Target Position just like on a normal position control axis.

Using a Virtual Axis as a Gearing Master or Curve Master

A virtual axis is typically used as a master axis that other axes can gear to or use a curve master. It is sometimes desirable to gear to a virtual axis rather than executing the motion as a function of time. All the axes geared to the virtual axis can be sped up or slowed down by speeding up or slowing down the virtual axis. The virtual axis can even be moved backwards causing the geared axes to back up too. This cannot be done using time-based commands.

When using a virtual axis as a master as described above, it is often useful to set it up as a rotary axis because it will never need to be reset. When used as a master, the virtual axis is typically commanded to move with a Move Velocity (37) command. Moving it at 1 unit/sec as the standard velocity makes gearing ratio calculations very easy. The acceleration and deceleration provide a smooth start and stop for the geared axis.

Setting Up a Virtual Axis

Add the Virtual Axis

To add a virtual axis to the RMC, use the Axis Definitions dialog:

Open the Axis Definitions dialog.
Whether you choose to change an existing axis or add a new axis, set the axis type to Virtual.
Click OK on the Axis Definitions dialog. If you are online, these changes will be applied to the controller. Make sure to update Flash and save your project.

Set up the Virtual Axis Parameters

A virtual axis has very few parameters. You need to set the Linear/Rotary parameter.

If you choose Linear, you will need to set the Positive and Negative Travel Limits.

If you choose Rotary, you will need to set the Position Unwind and Position Offset.

Once the virtual axis has been set up, you can issue closed-loop motion commands to it as to any position axis.