Curve Tool: Standard vs. Enhanced Curves

The RMC supports two types of curves: Standard and Enhanced. Each is described below.

Standard Curves

Standard curves were introduced with RMC CPU firmware dated 19971204. This gave the RMC the capability of following curves defined by cubic splines. The user defines the position and time (or master position) of each point in the curve. The velocities of the endpoints are fixed at zero (0). The velocities of all other points and accelerations of all points are computed by the RMC to find the smoothest curve through all points.

There are several deficiencies with Standard curves:

Because the accelerations are computed at the endpoints, it is likely that they will be non-zero and therefore result in an acceleration discontinuity and relatively high jerk at each endpoint.
It is difficult to accurately approximate a linear segment.
It is difficult to set and maintain a given velocity at a given point.
The velocities at the endpoints could not be changed from zero (0).

These issues prompted the introduction of Enhanced curves.

Enhanced Curves

Enhanced curves were introduced with RMC CPU firmware dated 20010208. They greatly enhance the capabilities of the RMC in following an arbitrary curve, and further enhance the smoothness of the curve.

The following items are introduced with enhanced curves:

The accelerations at the endpoints of a curve are always zero (0). Therefore, there is no acceleration discontinuity and therefore much lower jerk at the end points. The acceleration is continuous over the entire curve, even with the additional features listed below.
Segments can be easily designated as linear segments, which makes them exactly linear. This greatly simplifies camming and flying cut-off applications.
Any point, including the endpoints, can have its velocity set to a specific value. This, too, simplifies camming and flying cut-off applications.
Curves can be set up to auto-repeat, meaning that the curve restarts automatically when it reaches its end. See Auto Repeat Curves for details.

The drawback of Enhanced curves is that they can currently only be downloaded to the RMC through RMCWin, and not through communications modules such as Ethernet, PROFIBUS, and Modbus Plus.

You should always use Enhanced curves unless you are running firmware prior to 20010208 and do not wish to upgrade, or you need to download curves through the communication module.

To toggle a curve between Enhanced and Standard:

On the Tools menu, click Options.
Click the General tab.
Find the check box on the row of the axis you want to change under the column labeled Enhanced Curve. To make the curve for this axis Enhanced, set this check box. To make this curve Standard, clear this check box.
Click OK.