Tuning Overview

Once your system is set up and ready for use, it must be tuned in order to control it. Tuning is the process of adjusting the tuning parameters for optimum control of the system. The better tuned a system is, the closer the actual movement follows the desired path of movement.

Why is Tuning Necessary?

Tuning is required for moving an axis in closed loop control. In closed loop control, the RMC generates a target profile. The tuning parameters (gains) then dictate how much Control Output the RMC should generate each loop time in order to get the Actual Position to follow the target profile as closely as possible. The gains must be properly tuned to achieve precise motion.

On a well-tuned system, the Actual Position will closely follow the Target Position. To see a plot, click here.

On a poorly tuned system, the Actual Position will not follow the Target Position very well. To see a plot, click here.

Tuning Wizard and Autotuning

The Tuning Wizard makes the tuning process very easy. The Tuning Wizard provides autotuning and tuning based on existing plot.

Autotuning

Autotuning automatically moves the axis and then provides a range of gains from which you can choose with a simple slider bar. The RMC autotuning can be used on many systems. Even if autotuning is used, the user should posses a solid understanding of manual tuning to ensure proper tuning.

Autotuning can be used for position axes, including rotary and linear axes, and motors in velocity mode or torque mode. Autotuning does not support velocity, pressure, or force axes, although pressure or force axes can be tuned using an existing plot as described below.

See the Autotuning topic for details on how to perform autotuning.

Autotuning may not work for every situation. If it doesn't work for tuning your axis, you can use Tuning Wizard with an existing plot, as explained below.

Tuning Using an Existing Plot

If your axis cannot be autotuned, use this method to tune your axis:

Tune the axis using only the Proportional Gain.
Increase the Proportional Gain until the axis tracks well.
Move the axis in both directions, making sure to get a plot of each direction of motion.
In the Tuning Tools, click the Tuning Wizard button.
In the wizard, choose Use Existing Plots and continue.
In the wizard, choose the two recent plots you made of motion.
Complete the wizard, and the Gain Calculator will open. Now you can choose gains and move the axis.

See the Tuning Wizard topic for more details.

Note: Plots chosen for the Use an Existing Plot method should have been captured in capture mode. Do not use plots captured in trend mode, as they can cause inaccurate results.

Manual Tuning

Manual Tuning Procedures

Tuning procedures differ depending on the type of system. Please read the Tuning Guidelines below before continuing to any of the tuning procedures. Click the following links for suggested tuning procedures:

Tuning a Hydraulic Position Axis or Motor in Velocity Mode- the most common tuning procedure
Tuning a Motor in Torque Mode
Tuning Position-Pressure or Position-Force
Tuning Pressure/Force
Tuning Active Damping and Acceleration Control
Tuning a Pneumatic System

Manual Tuning Guidelines

Keep the following guidelines in mind throughout the tuning procedure. There is no substitute for experience when tuning an axis. The procedures offer some guidelines, tips, and suggestions for tuning your system. While the steps will work for many systems, they may not be the best for a particular system.

Use the Tuning Tools
The Tuning Tools in the Plot Manager provide a single place where you can issue repeated commands and change and download gains. In addition, plots are automatically uploaded after a command.
Reiterate these Steps:
The tuning procedure is a reiteration of the following general steps. Use these steps throughout the tuning procedure:

1. Make a move
  Typically, this is done using the Move Absolute (20) command. The Tuning Tools provide two buttons to easily issue two commands, typically one for each direction.

Tip:
For a typical hydraulic cylinder, the Accel and Decel parameters of the Move absolute command should be on the order of 20 -100 pu/sec2. The speed is typically between 1 and 30 pu/sec.

1. View the Plot
  When you issue a command in the Tuning Tools, the plot is automatically uploaded from the RMC. The plot will help you determine which parameters must be changed.
  In the Tuning Tools, you can easily disable the automatic plot upload for one of the command buttons. If you are focusing on tuning a certain direction, you can keep the plot from uploading when moving the other direction.
2. Change a Tuning Parameter
  Change a gain in the Axis Parameters section of the Tuning Tools. After changing the value you must click the download button or press Ctrl+D to download the changes to the RMC.
3. Repeat these steps
  Repeat these steps until the parameter is at the desired value.

Use the Mean Squared Error
The Mean Squared Error in the RMCTools Plot Manager can help determine how the last parameter change affected the system. The Mean Squared Error provides a rough indication of how closely the Actual Position is tracking the Target Position. If this number decreases significantly, the last parameter change was good. If this number increases significantly, the last parameter change was bad.

Start with Long, Slow Moves, then Use Faster Moves
Begin the tuning procedure with fairly long, slow moves and low accelerations. This will prevent you from losing control of and potentially damaging the system. The moves should be short enough to fit in the plot.
After gaining control of the system, you should increase the speed to values you expect to use during machine operation. Always tune your system at the speeds of intended operation.
Set Auto Stops
You may want to turn off some of the Auto Stop bits. The Auto Stops cause the axis to halt if an error occurs. In the initial stages of tuning, a Following Error or other error may occur, causing an undesired halt. Setting these bits to "Status Only" will make the RMC ignore the errors so you can tune the axis. Once you gain sufficient control of the axis, set the Auto Stop bits to halt. Turning off the Auto Stops may not be possible on some systems because of safety concerns.
Update Flash and Save the Project
When editing the parameters in the project, you must download them to apply the changes to the RMC. However, they are not updated in the RMC's Flash memory until you issue an Update Flash command. This will save the parameters even if power is disconnected. To save the RMC's parameters to the project, upload the parameters from the RMC and then save the project.