Identical Motion on Multiple Axes


#1

This topic describes how to perform the type of synchronized motion where all the axes always need to be at identical positions. This procedure assumes the axes are all identical, that is, the cylinders, valves, and feedback are all identical.

  1. Use the Move Absolute Command
    Send the same Move Absolute (20) command to the axes at the same time. This can be done in a user program. In the Command Tool, this can be done by typing in commands in all the pertinent axes, the clicking the Send All button. If the Send All button is not visible, right-click in the Command Tool and choose Show Toolbar.

  2. Plot
    Set up a plot template to include all the axes. The most important information is the Target and Actual Position, Control Output, and Target and Actual Velocity. Use this plot template as you do tuning. If you have many axes, and can’t fit everything on the plot, you can change the velocity so that it is not received directly from the RMC, but is instead calculated from the position. This makes it possible to have more items in the plot. To do this, in the Plot Template Editor, click New Quantity to add a quantity to a plot template, then choose the Advanced tab and in the Type of Formula, choose Rate of Change. Choose a position so that the plot will calculate its velocity.

  3. Use the Halt Group Axis Parameter
    In an identical synchronized system, if one axis halts due to an error, you need to make sure all the axes halt. Use the Halt Group parameter to do this. This parameter is in the Axis Parameters, on the All tab, in the Halts section. A value of zero means the axis is not in a halt group. For each axis that needs to be synchronized in a group, set its Halt Group to the same value, such as one.

  4. Tuning Setup
    When tuning, you will need to send identical commands to each axis to move between two positions. Here is one method:
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    [*]Make a user program with one step that sends one Move Absolute (20) command to all the axes to move to a position.

  5. Make another user program with one step that sends one Move Absolute (20) command to all the axes to move to another position.

  6. In the Tuning Tools, set up the two buttons to send a Start Task (90) command such that the one button runs one user program and the other button runs the other user program.
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    [
    ]Tuning Prodedure
    Also, during tuning, you cannot use the autotuning. You can however, use the Tuning Wizard once you get enough motion to get a plot. And, you must always set the gains for all axes each time you change the gains. Here is the basic procedure:

  7. Throughout this procedure, always use the Axis Tools Tune tab to set the gains of each axis identically.

  8. Set the Proportional Gain to some small value, then move the axes.

  9. Increase the Proportional Gain until the Actual Position is starting to follow reasonably well. The Actual Position should be parallel the Target Position during the middle part of the move. Once this happens, make sure to get a plot from the motion in each direction.

  10. Start the Tuning Wizard and choose Existing Plot. When you complete the wizard, slide the slider bar to where the Proportional Gain is about at what you already had it. Set the gains and feed forwards of all the axes to those values, then move the axes to see how they control. If you need better control, move the slider bar up, set the gains and feed forwards, and move the axis. Repeat until the axes control properly.
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#2

Why not use the Command: Sync Move Absolute (13)?

It is better than using “Send the same Move Absolute (20) command to the axes at the same time.”


#3

The Sync Move Absolute can certainly be used, but it doesn’t really offer any advantages on a system where the axes must always be identical. The Sync Move is designed to do synchronized ratioed moves, where the axes start and/or stop at different positions.