6. Programming with the Camera Locate Node

Fast Cycle Time

If the ambient lighting is stable during run-time, you can enable the fast cycle time configuration. To do so, go to the Installation tab from the program. Choose Camera and go to Configurations.

Fig. 6-1: Enable fast cycle time when ambient lighting is fixed.

By enabling the fast cycle time configuration, the camera exposure will be set the first time the program enters a Camera Locate node – at runtime. For all other Camera Locate nodes, the camera will keep the exposure settings from the first run. This reduces the cycle time by half as opposed to not enabling the fast cycle time configuration.

Fig. 6-2: Fast cycle time configuration.

Programming

The first thing to do after completing the object teaching is to add a Move node to the Snapshot position. When you exit the object teaching wizard, the robot arm is already in the Snapshot position location. You can simply add a MoveJ command before the Camera Locate node and set it to the location the robot arm is at (see Snapshot_pos_1 from the next figure).

The Camera Locate node acts as an "if" statement. If the taught object is detected by the camera, the robot program will enter in the Camera Locate node and execute all the command lines within it.

After teaching the object within the Camera Locate node, you may continue the programming by using either a linear move (MoveL) with the snapshot position's variable as feature or the object_location pose. It is also possible to edit the detection threshold or the saved object position after the Teach Object wizard.

• Refer to Section 6.1 to program a robot motion with a linear move (MoveL) with the snapshot position's variable as feature. This allows to perform robot motion relative to the object detected at run time.
• Refer to Section 6.2 to use the object_location pose to program the robot motion - for advanced use.
• Refer to Section 6.3 to edit the detection threshold and/or the saved object position.

6.1. Linear Move with Feature

Once the Teach Object wizard is completed, you saved the last position of your object. The object position variable, named after the snapshot position, now contains the reference frame of the object in this saved position. Each time the Camera Locate node localizes an object, it updates that feature variable's frame with the new detected object's position and orientation. That feature is named according to the feature name you chose during the snapshot position definition.

You can use that reference feature inside the Camera Locate node within Move commands of the robot. To do so:

• Insert a Move node.
• In that node, go to the Command tab.
• Select MoveL.
• Select the appropriate feature (your Snapshot Position / Feature name).

Every waypoint inserted within that MoveL node will be relative to the feature updated by the Camera Locate.

6.2. object_location pose

Once a snapshot position is defined, the workplane used for the calibration gets its own coordinate system, regardless of its orientation. This coordinate system is shown in the figure below.

Fig. 6-3: workplane reference frame.

The camera will detect an object on the workplane and find its X-Y position, as well as its Z-orientation in the workplane's coordinate system (see figure below). Thus, a detected object is always laid flat (parallel) to the workplane. It is possible to use the object_location pose, which is a variable containing the detected object's pose (p[x, y, z, x rotation, y rotation, z rotation]) in the robot's base reference frame. This variable is updated each time the program goes within a Camera Locate node, thus every time an object is detected, regardless of how many Camera Locate nodes are in the program. The object_location pose is relative to the robot's base frame.

Fig. 6-4: object_location pose on the workplane used for the calibration.

object_location is a variable with the pose structure (x, y, z, x rotation, y rotation, z rotation):

x: x position of the object detected, relative to the robot's base reference frame.

y: y position of the object detected, relative to the robot's base reference frame.

z: z position of the object detected, relative to the robot's base reference frame.

x rotation: x rotation from the robot's base frame to the detected object feature reference frame. The object's X axis is parallel to the workplane on which the calibration has been performed.

y rotation: y rotation from the robot's base frame to the detected object feature reference frame. The object's Y axis is parallel to the workplane on which the calibration has been performed.

z rotation: z rotation from the robot's base frame to the detected object feature reference frame. The object's Z axis is normal to the workplane on which the calibration has been performed, points downwards from it, into the workplane.

Program Example

The program examples below show how to use the object_location pose variable.The first one simply moves the robot so that the TCP goes directly on the detected object. Make sure the TCP is set properly to avoid collisions.

Fig. 6-5: Program example - place the TCP on the detected object.

The second example moves the robot so that the TCP goes 20 cm above the detected object. This is in the case of an horizontal plane.

Fig. 6-6: Program example – Place the TCP 20 cm above the detected object, in case of an horizontal plane.

6.3. Edit Detection Threshold and Object Location

It is possible to edit both the detection threshold and the object location after the Teach object wizard has been completed. To do so, select the Cam Locate node, go to the Command tab and tap Test/Modify.

• To modify the saved object position, place the object in the desired position. Test is with the Test locating object button and, when in the desired position, tap Define new position. The position is saved. Tap Save & close to exit the wizard. This also saves the threshold.
• To modify only the detection threshold, modify it and test it. Once it is at the required value, tap Save & close. This does not modify the object position previously saved.
• To modify both the threshold and the object location, adjust the threshold, place the object in the desired position and test is with the Test locating object button. Once in the desired position, tap Define new position. The position is saved. Tap Save & close to save the threshold.

6.4. Camera Locate node at a variable Snapshot position

During a robot program, the robot must be at the snapshot position before entering the Camera Locate node. If it is not in the right position, a pop-up will appear, preventing the camera from taking a snapshot from the wrong position. This is to ensure good precision since the workplane has been previously calibrated for this snapshot position.

In some cases, it is helpful to move the robot to a variable position to enter a Camera Locate node. For instance, it can also used to teach only one snapshot position and object to manage parts in stacked trays. In order to do so, allow the robot to be in a different position that the original snapshot position by entering the script command:

ignore_snapshot_position = True

You also need to edit the snapshot_position_offset pose variable. This variable contains the pose offset between the original saved snapshot position and the one used in the program .

The example shows a program using a Camera Locate node to manage parts in stacked trays.

• The script command in the BeforeStart section allows the camera not to be in the exact snapshot position when entering a Camera Locate node.
• The pose at which the robot enters the Camera Locate node is calculated knowing how many trays are stacked.
• The snapshot_position_offset is calculated accordingly in order for the Wrist Camera to consider the pose offset from the original snapshot position.

Fig. 6-7: Program example.