Robot Positioning System

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Introduction

Robots in the Rethink Robotics Family are designed to be deployed quickly between tasks or work cells. This design is a beneficial one but it also introduces a whole new set of challenges for robotics. For example, moving robots from one work cell to another means the locations of Pick, Place, and Hold actions for a task must be adjusted in the new work area. When human operators accidentally bump into tables, conveyors, or the robot, the physical location of picks or places will no longer match what is saved in the robot and these slight variables can cause the robot inaccurate pick and place objects.

For this reason the Robot Positioning System has been built into the Intera Platform. In a new workflow using this feature, an operator can quickly re-register the robot to the workspace and continue working without having to retrain a task or spend time trying to fine-tune a previously trained task.

Note: At present the Robot Positioning System only works while the task is being trained; it does not dynamically adjust as the robot performs the task.


The following page pertains to both Sawyer and Baxter Robots.

Landmarks

Landmark.png

A landmark is a fiducial marker placed in the field of view of an imaging system to be used as a point of reference. Rethink Robotics currently supplies landmarks on anodized aluminum with an adhesive backing that can be placed on the surface of modules in the work area.

If your robot -- or the surface containing the landmark on which an action takes place -- moves, you can use the Robot Positioning System to re-register the action in relation to the original location and quickly reorient the robot in relation to the task.

Note: This feature is designed for relatively small changes in location. The movement between the original location and the re-registered one should not be more than a distance +/- 50mm and/or a rotation of 10 degrees.

IMPORTANT: Best Practices

  • Assign every action in a task to a landmark.
  • Use unique Landmark numbers for each module and for each arm.
  • Make sure Landmarks are placed on a flat, horizontal, leveled surface and that the surface is properly cleaned before placing the landmark.
  • Do not reuse Landmark numbers in the same task.
  • Place the landmark as close as possible to the location where an associated action takes place.

Using Robot Positioning System

After a task has been created with accurate pick, place, and hold locations, the actions locations can be associated with Landmarks that are placed in the workspace of the robot. The instructions below describe the how to register a Landmark in the robot workspace and how to associate a registered Landmark with a saved action.

IMPORTANT: Best Practices

  • Make sure there are no obstructions between the end of arm camera and the landmark.
  • Make sure Landmarks are placed on a flat, horizontal, leveled surface and that the surface is properly cleaned before placing the landmark.
  • The further away a landmark is from the actions, the less precise it might be when reregistering the robot. Rethink Robotics recommends landmarks be no further than 50cm away from the actions associated with them.
  • Confirm none of the joints are near their limit. This is shown by a red bar corresponding to the joint on the left side of the screen in modify. See Joint limit indicator
  • To allow the robots' imaging system to see the landmark, position the end effector camera approximately 20cm above the landmark, with the landmark in the center of the field of vision. The gain may also need to be adjusted to ensure there is sufficient light for the camera to view the landmark.

Registering a Landmark

  1. The process of adding a new landmark can be started using two different methods.
    • Method 1: On the Task Map, press the action button on the training cuff and select Landmark from the submenu.
    • Method 2: Press the Rethink button on one of the navigators and scroll to the landmark option to open the landmark gallery.
    • Once the landmark gallery is open, scroll to and select "Create New".
    I33 RPS Landmark Gallery Create New.png
  2. The "Create a Landmark" window will open. Position the arm approximately 20cm above the landmark, with the landmark centered in the camera's display.
    • The camera in the arm will turn on and will recognize the landmark and highlight it with a green outline.
    • If Baxter cannot locate the landmark, as in the example below, do one of the following:
    • Make sure the camera is 20cm above the landmark
    • Adjust the gain and lighting to make the image brighter or darker
    • Remove the end effector if it is causing obstruction with the camera view

    I33 RPS Cannot Locate Landmark.png

  3. The strength of the recognition is displayed by the height and brightness of the vertical green bar in the middle of the screen: taller and brighter = stronger recognition. The landmark is recognized when it is outlined in green and a message displays with the landmark's number, as in the example below.
  4. I33 RPS Recognized Landmark.png

  5. Save the landmark by selecting Save. To avoid moving the camera, press the OK button on the torso, base, or other arm (when using the Baxter robot).
  6. When the landmark is saved, the screen displays a check mark and the number of the landmark as shown the image below.
  7. I33 RPS Landmark Successfully Registered.png

Associate a Landmark to an Action

Landmarks can be associated from the modify panel of an action or from the landmark gallery.

From the Modify Panel

  1. Select the action on the Task Map.
  2. Select the add (+) button Plus.png and then select the landmark button Landmark7.png
  3. The Associate Action to Landmark screen is displayed.
  4. I33 Associate Action To Landmark.png

  5. Select the landmark for the action.
    • In this example, landmark 7 is associated with Pick 1B
  6. Press OK and then press the back button 3 times to return to the task map.

From the Landmark Gallery

Note: Multiple actions can be associated to a single Landmark when using the Landmark gallery. This is a more efficient approach when there are multiple actions that need to be associated to Landmarks.

  1. While in the Task Map, press the Rethink button and select the landmark gallery icon.
  2. Select the Landmark that will be associated from the gallery and then select "Associate with..." from the menu.
  3. I33 RPS Associate With.png

  4. From the list of actions, check off the actions that will be associated with this landmark by scrolling to the check box and pressing the OK button on the navigator.
  5.   Note: When associating multiple actions on Baxter, only actions trained on the same arm with which the landmark was registered can be selected.
    
  6. Once all of the actions that will be associated with the landmark have been selected, press the back button twice to return to the main screen of the landmark gallery. The actions selected will now be listed in the "Associated with" window in the gallery as seen in the image below.
  7. I33 RPS Associate Landmark Gallery.jpg

How to Reregister a Landmark

After one or more of the action locations has been moved -- whether because the robot has been moved, a fixture has been inadvertently bumped, the robot has been inadvertently bumped, etc. -- it's easy to re-register the actions using the Robot Positioning System.

IMPORTANT: Best Practices

  • When re-registering to a previously associated landmark, it is very important to not move the arm from the original location. Doing so will introduce error into the associated actions. Therefore, it is recommend that the navigator on the torso, base or opposing arm is used to press the OK button.
  • For certain tasks it may be required that landmarks be mechnically fixed to the workspace. For example: tasks where the surface is particularly hot, which would affect the adhesive on the landmark, allowing it to drift.
  • If you have previously registered a landmark and the workspace has changed dramatically since the robot last performed the task, the robot may not be able to reach one of the actions even after reregistration. The best course of action is to assemble the workspace so that it reflects the original setup as accurately as possible. Otherwise, in order accurately reregister the robot to the workspace, it is recommended to start with one location and adjust the workspace if necessary. Once the registration process on the first location has been completed, start reregistering the second and adjust the workspace if necessary. If any movement affects a previously reregistered location, that location may need to be updated to reflect the workspace changes.

Reregister

  1. Press the Rethink button and select the landmark gallery from the button bar.
  2. Select the landmark to be reregistered and then select "Reregister" from the list of options.
  3. I33 RPS Reregister.png

  4. Press Start.
  5. I33 RPS Start Reregister.png

    • The arm moves to its original location.
    • A gray outline indicates the location where the landmark was originally saved.
    • If the new location of the landmark is no more than 50mm and/or 10 degrees rotation from the original landmark location, Baxter will recognize the new location.
    • If the new location is too far off, just move Baxter or the module until the green outline is displayed.
  6. Press Reregister. The grey ghost image of the landmark shows the outline of the first original trained position of the landmark. This image does not update each time the landmark is re-registered. For best performance it is recommended that the current location of the landmark be varied less than +/- 50mm and/or a rotation of 10 degrees. If the position has greater difference than this, it is recommended to move Sawyer or the interacting surfaces to align the landmarks more closely
  7. I33 RPS Reregister New And Old Locations Shown.png

  8. The landmark is reregistered (note the checkmark) and the location is realigned with the original task location.
  9. I33 RPS Landmark Successfully Registered.png

  10. The software will automatically return to the landmark gallery. Press the back button twice to return to the task map.

Video

FAQ

Q: I tried registering a landmark, but I get a message that says “Multiple landmarks are visible.” What should I do?

A: The robot is seeing more than one landmark. Cover one of the landmarks with your hand until just one is recognized. Then, press Save and keep your hand covering the other landmark until the desired landmark is saved.

Q: I registered a landmark but now I would like to remove it. What do I do?

A: Select the action whose landmark you’d like to remove and go into the landmark gallery panel as described above. Once in this gallery, select and the landmark will be de-associated from that particular action.

Q: When I relocate the robot, will my custom paths be erased?

A: No. The path will remain the same but the end points (i.e. Approach/Retract) will move to the new locations.

Q: When I have Action Groups, do I need to associate each action to a landmark or may I just associate the whole Action group to the landmark?

A: If you have an Action Group and would like to associate all actions to a landmark, you can just associate the whole Action Group in one step.

Q: Are there any special lighting requirements for using landmarks?

A: Recognition of landmarks works best with soft, diffused lighting that does not produce hard shadows.

Q: Does the landmark need to be trained at the same orientation as the pick or place action?

A: No. You could have your landmark mounted horizontally to the frame of the conveyor even though the robot will pick in an off-vertical orientation on the conveyor.

Q: Can a landmark be associated with a Hold?

A: Yes.

Q: What do I do when a landmark is damaged?

A: Replace it with a new landmark and use the Overwrite feature in the landmarks gallery. Remember to overwrite the Landmark before removing it from the workspace.

Q: What do I do when I need to associate waypoints in a path to a Landmark?

A: It is not currently possible to associate paths to a Landmark.