How to Re-Establish 3D ETH Relationships After Movement

Examples are valid for :
TMflow Software version: All versions
TM Robot Hardware version: HW3.2 or above versions
Other specific requirements:
•    3D camera
•    Landmark
•    Robot with 2D Camera
Note that older or latest software versions may have different results.
 

Purpose

•    We can establish the relationship between the robot and the 3D camera through ETH calibration, as illustrated by the green line in the figure below.
•    If the robot or the table is moved, this will alter the relationship between the 3D camera and the robot, as shown by the red line in the figure below. In this case, the relationship becomes unknown.
 

•    At this point, we can fix a landmark at one corner of the table and use the position of the landmark to re-establish the ETH relationship between the 3D camera and the robot.

Definition of Symbols 

• ^BT_A  represents the transformation relationship from A base to B base.

• ^AP_object    represents the position of an object in A base 

Advantages of Built-in Vision for the Robot

Base Transformation Relationship

Fixed Robot Base/Camera 

Under normal circumstances, we can obtain the relationship ^RobotT_{3D Cam} (3D ETH Camera Calibration)through ETH calibration, which defines the workspace.

• Through vision job in TMflow, we can obtain ^RobotP_object, which represents the position of the object in the Robot Base.
• At this point, the relationship ^{3D Cam}T_world  is unknown in TMflow. We need to derive ^{3D Cam}T_world  using ^RobotT_{3D Cam} and ^RobotP_object. This derived relationship describes the object’s pose in the 3D Camera Base.
• The relationship is as follows:

Before Moving- Unfixed Robot Base/Camera

•    Place the landmark at a fixed position on the table.
•    Next, create a vision job to locate the landmark and obtain the Vision Base of the landmark, denoted as ^RobotT_LM. . The relationship is as follows:

• At this point, ^RobotT_{3D Cam}   and ^RobotT_LM    are known. To obtain the hand-eye relationship after moving, we must first determine the relationship ^LMT_{3D Cam}  before moving. The relationship ^LMT_{3D Cam} is as follows:

After Moving- Unfixed Robot Base/Camera

• Base on the settings before moving, the relationship ^LMT_{3D Cam} is already known. After moving, capture the LM again to obtain the new relationship of LM relative to the Robot ^RobotT^'_LM. . Combing ^RobotT^'_LM , we can derive the new workspace after moving, which is ^RobotT^'_{3D Cam}  . The relationship is as follows:

• Using the relationship ^RobotT^'_{3D Cam} in combination with ^{3D Cam}T_world , we can transform the object in the World Base ^worldP_object  to the new Robot Base, which is ^RobotP^'_object  . The relationship is as follows:

TMflow Configuration

Vision Job Localization 

•    After completing the ETH correction, it is necessary to instruct the picking position.
•    In step #1, acquire the vision job object’s vision base and variable “Base[“Vision_Find_Object_ModelCAD”].value”.
•    In step #2, teach the picking point “Prepick_Point” through the Vision base.

Fixed Robot Base/Camera

•    Under normal circumstances, we can obtain the relationship ^RobotT_{3D Cam} (3D ETH Camera Calibration) through ETH calibration, which defines the workspace.
•    Through vision job in TMflow, we can obtain ^RobotP_object, which represents the position of the object in the Robot Base.
•    At this point, the relationship ^{3D Cam}T_world   is unknown in TMflow. We need to derive ^{3D Cam}T_world   using ^RobotT_{3D Cam}  and ^RobotP_object.. This derived relationship describes the object’s pose in the 3D Camera Base.
•    The relationship is as follows:

• Add a global variable “g_workspace” and record the calibrated ETH relationship in this variable.

• Add the variable “var_T_ObjectTo3DCam” to describe the transformation ^{3D Cam}T_world.

• After the vision job object localization, connect a SetNode next 

• Use the ‘changeref’ function to change the object's Vision base from Robot Base to describe it on the 3D Camera Base, and record this relationship in “var_T_ObjectTo3DCam”, which is ^{3D Cam}T_world 

Before Moving- Unfixed Robot Base/Camera

•    Place the landmark at a fixed position on the table.
•    Then, create a vision job to locate the Landmark and obtain the Landmark’s Vision Base and the variable Base["Vision_Find_LM"].Value. This relationship is denoted as ^RobotT_LM  , and the relationship formula is as follows:
 

• At this point, ^RobotT_{3D Cam} and ^RobotT_LM  are known. To obtain the hand-eye relationship after moving, we must first determine the relationship ^LMT_{3D Cam} before moving. The relationship ^LMT_{3D Cam}  is as follows:

• Next, create the global variable “g_3DCamToLM”

•    Use the ‘changeref’ function within the set node to change the description of the 3D Camera Base from Robot Base to Landmark’s Vision Base. This relationship is denoted as ^LMT_{3D Cam}, representing the pose of the 3D Camera in Landmark’s Vision Base.
 

• After executing these two nodes, which are the preparatory steps 

• Once the setup is completed, ^RobotT_{3D Cam} becomes a known value as well.

After Moving - Unfixed Robot Base/Camera 

• Base on the settings before moving, the relationship ^LMT_{3D Cam}  is already known. After moving, capture the LM again to obtain the new relationship of LM relative to the Robot ^RobotT^'_LM.  . Combing ^RobotT^'_LM , we can derive the new workspace after moving, which is ^RobotT^'_{3D Cam} . . The relationship is as follows:

• Using the relationship ^RobotT^'_{3D Cam} in combination with ^{3D Cam}T_world, we can transform the object in the World Base ^worldP_object  to the new Robot Base, which is ^RobotP^'_object  . The relationship is as follows:

• Set the initial position to a location where is can capture the Landmark
• First, set the Landmark’s vision job  before the object’s vision job  , as shown in the diagram.

• Add the variable “var_new_workspace” to describe the relationship ^RobotT^'_{3D Cam} 

• In the previous ‘Set_update_ETH’ set node, use the ‘changeref’ function to change the pose of the 3D Camera described in landmark’s Vision Base to Robot Base. This action establishes the relationship ^RobotT^'_{3D Cam},, representing the new Workspace.

•    At this point, the relationship ^RobotT^'_{3D Cam}  is also known, indicating that we have obtained a new Workspace.
•    Next, by combining the new Workspace ^RobotT^'_{3D Cam}  with the  transformation ^{3D Cam}T_world , we deduce the object’s new position in Robot Base ^RobotP^'_object , which is the object’s new Vision Base. Similarly, using the ‘changeref’ function, we convert the object’s pose described in the 3D Camera Base to Robot Base, obtaining ^RobotP^'_object.
•    Finally, record this relationship in the variable ”Base[“Vision_Find_Object_ModelCAD”].value” of the original object’s Vision Base to update the Vision Base accordingly.

Execute the Project 

Finally, execute this project. The process flow is shown in the diagram below. The picking point ”Prepick_Point” will be updated according to the movements of the camera or the robot base.