Linear interpolation error

Created by Dennis Trapp, Modified on Fri, 18 Feb, 2022 at 10:03 AM by Rico Stodt

When creating a Move To node, the default "move type" in the node inspector is "joint".  This means that all of the joints will move in some fashion to position the tool center point (TCP) in the new location.  The TCP will move in an arc or series of arcs on its path.  However, there are times when you need for the TCP to move in a straight line, for example when reaching into a box or inserting a part into a fixture.  This is when you would change the move type to "linear".  Linear moves are a much more difficult problem for the robot to solve because it needs to figure out how to move all 7 joints simultaneously so the TCP moves in a straight line.  Sometimes, it can't do so and a linear interpolation error occurs.

When a task is running, if there is no error handling, the robot will stop and display the error message on the screen.  If you are working in Intera Studio and open the Move To node, and click "Test" (which is supposed to make the arm move to that postion), nothing happens, and there is no error message.

You might even get this type of error when it seems possible to move in a straight line.  Our controls engineers are actively working to make improvements in this area for future software releases.  In the mean time, here are some best practices.

  • Only use linear moves when necessary
  • Keep them to as short of a distances as necessary
  • If an error is encountered, break the move up into 2 separate moves.  The downside is there will be a brief pause between the moves
  • Reduce the linear and rotation acceleration parameters in the Move To node.

Also note that it is also possible to encounter joint errors when using a "joint" move type as well.  This often happens when the joint positions are drastically different than the desired position.  When this happens, create one or more intermediate Move To nodes between the current and desired postion.  If you are working in Studio and press the "Test" button and nothing happens, manually move the arm using the zero-G button to make it closer to the desired position.

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