3. Adding a Workstation
Cell Editor Walkthrough
This tutorial is part 3 of a 5-part walkthrough on creating your first cell in the verbotics cell editor. It acts as an introductory guide to cell editor, and it is recommended you complete all 5 walkthrough videos before viewing the proceeding tutorials.
In this tutorial, we’ll be creating a workpiece positioner to be used in tangent with our robot as a workstation.
Prerequisites and Resources
This walkthrough uses a workstation model which can be downloaded here.
This walkthrough continues on from part 2’s cell, if you lost or didn’t save that cell, download the example cell here to continue on with this tutorial.
Video Tutorial
Step by Step Guide
Introduction
This 5-part walkthrough takes you through creating a cell from scratch for use in Verbotics Weld. This third part will explore the creation and model configuration of a workpiece position.
Step 1: Adding a Workstation
Importing the Workstation Model
Start by importing the workpiece positioner STEP model. Using the import step function, locate and import the ABB Workpiece Positioner file.
Sometimes, the model may be imported into a position which overlaps with other cell components. Hence, go ahead and reposition the workstation to be located in front of the robot.
While when creating the robot in the first part of the walkthrough, the create robot function to generate the robot’s kinematics. For workstations and other cell components with moving joints, you’ll need to manually ensure the origin of each of the joints are positioned correctly.
Many manufacturers will already have the origin of their positioners joints in place when you import the model. However, it’s vital to double check the positions kinematics.
Preparing Workstation Kinematics
Navigate to the URDF tree and expand the “imported” branch. You’ll see the model has been imported and split into 5 different joints. In order to prepare these joints correctly, the 5 joints need to be simplified into 1 base joint, and 2 rotating joints. Additionally, its important to make sure the origin of the 2 rotational joints are positioned at the centre of where the joints should be rotating around.
Imported Workstation Tree
Start by locating the 2 base joints, and selecting the mesh contained within both. Now merge these by right clicking, then select merge.
Now move onto the arm joint. Repeat the same steps as before, selecting the 2 arm meshes then merging. Now, as the arm is connected to the base, drag and drop the arm joint containing our mesh into the base link.
Make sure to click yes to all when prompted with the “retain global position” dialogue, which ensures the model doesn’t move after rearranging the cell’s tree layout.
For the last joint, the platter, there is only 1 model. As such, simply drag and drop the platter joint into the arm joints link. Once again selecting yes to retaining the global position.
Step 2: Adjusting Origins and Preparing Motion
Adding motion to joints manually requires several tasks to be completed. Including:
Changing a joint’s type
Entering joint limits and speeds into a joints properties
Ensuring origins are positioned correctly
Let’s apply this process first to the arm joint. Start by selecting the arm joint and navigating to its properties. Currently, the joint will have Fixed set as its Type.
Expand the drop-down box and change this to instead be Revolute. Now, several more parameters will be available to change, including axis, range and velocity.
Revolute Joint
Using the data given in the workpiece positioners data-sheet (data is shown below for simplicity), update the range and velocity values.
Joint |
Minimum |
Maximum |
Velocity |
Arm |
-180 |
180 |
90 |
Plate |
-360 |
360 |
150 |
However, attempting to jog the joint will show that the arm does not move as expected. This joint needs its origin repositioned and its axis updated to be correct.
First, the origin needs to be fixed. The origin needs to be at the centre of where our arm joint connects to the base. There are multiple methods to locate this point accurately:
Often, models will already have the correct origins, sometimes however, this origin will be attached to the connecting joint, instead of the joint in motion.
Locating the model diagram from the workstation manufacturer
Sort through the 5 joints that were imported earlier, you should find that base_joint_2’s origin matches to where we need the arm_joints origin.
To change the arm_joint origin to match base_joint_2, select the arm_joint then set the manipulation mode to origin in the right pane.
Now, click on the Copy transform from button, then click on base_joint_2 in the viewer. Upon doing this, you should find that arm_joint’s origin has been repositioned correctly.
Copy Transform From Function
The last step is to set the axis parameter. With the arm_joint selected, you should find the green arrow sits in the dead centre of the point the arm should rotate around. The green arrow represents the y axis, as such set the axis to be y.
Reattempting to jog the arm joint should result in an expected motion.
Now repeat this process for the platter joint.
Navigate to the platter joint and select it. Notice that unlike the arm joint, the platter already has its origin set correctly.
Set the platter’s type to be revolute, then set the axis to be z, as with the joint selected we can see a blue arrow representing the z axis pointing along the axis we want our joint to rotate around.
Plate Origin and Axis
Set the minimum and maximum to –360 and +360 respectively, and from the data sheet, we can see the speed should be set to 150.
And with that, our revolute joints and kinematics are all ready to go. However before moving onto the next step, let’s go ahead and place our workpiece positioner onto our cell’s base link, then tidy up our work tree by removing all the remaining unused links.
Step 3: Adding a Workstation TCP
In order for verbotics weld to identify where parts should be placed on the workstation, a tool centre point link is required. This requires a tcp joint and link to be created under the workstations platter link. Navigate to the link containing our positioners platter then create a joint and a link, naming them workstation_tcp_joint, and workstation_tcp_link respectively.
This joint and link MUST NOT contain any additional bodies, joints or links, as this can otherwise cause errors when trying to use the cell in Verbotics weld.
This is the final link needed for the workstation. As all the required joints and links have been created, select all of our workpiece positioners joints then create a new joint group. Name this new joint group “Workstation” as this this will be used later to inform verbotics which joints make up the workstation.
Step 4: Preparing Collisions
Adding Collision Bodies
Start by selecting all the meshes making up the workstation and open the create bounds function in the right-click menu. For simplicity, set shape to mesh and the decomposition quality to course.
Note
The method used above, while successfully generating the required bounds very quickly, is likely to cause performance issues in Verbotics Weld. We recommend watching our Cell Collisions tutorial after the walkthrough to better understand creating the most optimal collision bodies.
Once the preview of the collision bodies finishes loading, click create.
Collision Bodies Generated for Workstation
Disabling Collisions
As the workstation is now populated with collision bodies, next you need to analyse these collisions and disable any collisions occurring where joints are connected. Open the analyse collision function from the ribbon menu.
Before you run the collision analyser, first make sure to uncheck the start from scratch option. Start from scratch removes all current disabled collisions. As the cell has collisions already created for the robot and tool you’ll need to keep, this must be disabled. Once this is done, click go.
Analyse Collisions for Workstation
Once the results are visible, ensure to check the list to be certain there aren’t any unexpected collisions you want to remain enabled, then click create to confirm all recommended links to have collisions disabled.
In addition to the collisions disabled via the collision analyser, you also need to ensure that collisions are disabled between our workstation tcp and our workstations platter. If this isn’t disabled, when you import a part when using this cell in weld, you’ll find weld identifies the part as a colliding with the platter, even though it’s expected to be placed on the platter.
Start by selecting our workpiece platter, then in the links with collisions disabled box, search for the workstation tcp and then click add to disable collisions with that link.
Now, the workstation’s collisions are fully prepared.
Step 5: Finalising the Workstation
The final step is to finalise the station by creating a workstation in the model configuration and adding all the required parameters.
Navigate to the model configuration menu, and select workstations then “Add Work Station”.
In this new workstation, you’ll see several options and boxes which need updating with our workpiece positioners components. First, name this “Tutorial Workstation”.
Then, you’ll see the next you need to identify which group of joints represent our positioner. In the search box, search for and select our Workstation group you created earlier.
The final item you need to specify is the workstations tcp link. Which you can once again do by searching for “Workstation_tcp_link” and select the link once it appears in the search box.
Workstation Model Configuration
With that, the workstation model configuration is complete, and the workstation itself is ready to use in the cell.