Curve Tool: Converting a Plot to a Curve

Many applications that require the Curve Tool also require training the Curve Tool as to what the curves should look like. For example, some applications use a joystick to move some axes through a sequence, and then want to have the RMC play back that sequence. Other applications may have an existing control system that needs to be retrofitted with an RMC-equipped system, so the RMC should copy the existing movements.

The RMC excels in these applications. You will first need to capture a plot of the move you want to convert to a curve, then convert the plot to a curve, and finally clean up the curve. Each phase is described below:

To capture a plot for converting to a curve:

Set the Plot Time for the axis to indicate the number of seconds that the move you want to capture will take. Round up to the next largest whole number (or even number if you have RMC CPU firmware with a 2 ms control loop).
Initiate the plot capture at the same time you start the motion on the axis.

The most common way to start the plot capture in this situation is to issue a Start Graph (y) command on the axis that you want to capture.

You may want to use the Event Step table to issue this command to tightly couple the start of the graph with the start of the motion.

To convert a plot to a curve starting with the Plot window open:

Open a Plot window for the axis of the curve you want created, as described in Opening a Plot Window.
Either upload a plot from the RMC, or open a saved plot, as described in Reading Plot Data from the Motion Controller and Saving and Restoring Plots.
On the Data menu, click Convert Plot to Curve.

The Curve Tool will be opened or brought to the foreground. You will be prompted for the conversion interval.

In the Convert Plot to Curve dialog box, type the number of milliseconds that you want between each point in the curve.

The shorter this interval, the more difficult it will be to edit the curve later and the higher the accelerations will be, but the more accurately you will follow the curve. The longer this interval, the easier it will be to edit the curve, but it may not following the original plot as well. It is worth trying several conversion intervals to find the optimal interval.

Click OK.

To convert a plot to a curve starting with the Curve Tool open:

Open the Curve Tool.
Select the axis that has a plot you want to convert to a curve, as described in Selecting the Active Axis.
On the Online menu, click Convert Plot to Curve, or use the corresponding toolbar button ( $image\but_ptc.gif$ ).

The current plot will be read from the active axis. This will take a few seconds.

In the Convert Plot to Curve dialog box, type the number of milliseconds that you want between each point in the curve.

The shorter this interval, the more difficult it will be to edit the curve later and the higher the accelerations will be, but the more accurately you will follow the curve. The longer this interval, the easier it will be to edit the curve, but it may not follow the original plot as well. It is worth trying several conversion intervals to find the optimal interval.

Click OK.

Tips for Cleaning up a Curve

Avoid the temptation of specifying a short time between each point in the Convert Plot to Curve dialog box. This can make it nearly impossible to edit the curve and will often make the move jerkier by having so many segments with different accelerations.
Delete points in sections that have few inflections. This will help make these segments smoother with very little affect on the accuracy of the curve.
If a section of the curve is supposed to be linear, then delete all points in that interval, and instead set the point at the beginning of that section to be linear. See Selecting Linear or Cubic Segments for details.
You might want to try drawing your curve from scratch, using the uploaded curve only as a guideline. This is the best way to get the most accurate and smooth curve. In the steps below, we will assume that axis 0 is the axis that you read the plot from and on which you want the final curve, and that axis 1 is the temporary axis:
Convert a plot to a curve on axis 0. You can use a relatively short conversion interval when using this method to get the most accurate copy of the curve.
Copy this curve from axis 0 to axis 1. See Copying Curves between Axes for details on copying curves from one axis to another.
Ensure that both axes 0 and 1 are displayed. See Selecting Which Curves to Display for details.
Select axis 0 as the active axis, as described in Selecting the Active Axis.
Delete the curve on axis 0, as described in Erasing a Curve.
Add points to axis 0 to create a curve that matches the profile of the uploaded curve on axis 1.
You will need to create the new curve slightly above or below the uploaded curve to avoid grabbing points on axis 1 accidentally.
Add as few points as you can to match the uploaded curve. Drag the points as necessary to help match the curve.
Press CTRL+A to select all points in the axis 0 curve.
Drag the entire axis 0 curve until it is over the uploaded curve on axis 1.
Drag individual points in the axis 0 curve to match the axis 1 curve if differences show up after overlaying the curves.
Delete the curve on axis 1.