Programming Guide to Utility Behaviours
The utility IUB classes serve the following purposes.
Output information use for debugging
Scene manipulation use for simulation
Debugging IUB Classes
The following behaviour classes can be used in a behaviour tree for printing a message and other information.
Class task_trees.behavious_base.Print
This class extends py_trees.behaviour.Behaviour. It prints a message to the screen when ticked, and after that the tick will move to the next behaviour in the same Sequence or Selector.
class Print(Behaviour):
def __init__(self, msg, print_tree=False):
...
The parameter msg supports late binding through passing a function. The function should return a string message.
Class task_trees.behavious_base.PrintPose
This class extends py_trees.behaviour.Behaviour. It prints the psoe of the end-effector and the joint values, and after that the tick will move to the next behaviour in the same Sequence or Selector.
class PrintPose(Behaviour):
def __init__(self, arm_commander:GeneralCommander=None):
...
Class task_trees.behavious_base.PrintPoseInFrame
This class extends task_trees.behavious_base.PrintPose. It prints the pose of the end-effector in the given reference frame. The parameter reference_frame supports late binding through passing a function. The constructor requires the scene configuration model if a custom reference_frame is used.
class PrintPosesInFrame(PrintPose):
def __init__(self, arm_commander:GeneralCommander=None, scene:Scene=None, reference_frame:str=None):
...
Example:
The following code snipped is extracted from simple_move_3_printpose.py source code under demo/simple_moves.
def create_move_branch(self) -> Composite:
""" Returns a behaviour tree branch that move the end_effector to random positions
:return: a branch for the behaviour tree
:rtype: Composite
"""
move_branch = Sequence(
'move_branch',
memory=True,
children=[
Print('Before Random Move', print_tree=True),
DoMoveXYZ('move_xyz', True, arm_commander=self.arm_commander, target_xyz=self.generate_random_xyz),
PrintPose(arm_commander=arm_commander),
],
)
return move_branch
Notes:
The
Printbehaviour is specified to print the behaviour tree status in addition to a text message when it is executed. The text message can be replaced by a function reference that can return a message dynamically.The
PrintPosebehaviour is used to display the pose after the random move.
Simulation IUB Classes
The following behaviour classes can modify the robot configuration by attaching or detaching objects to the robot arm. It is useful for simulation such as grabbing and releasing an object in a simulated environment. Both of these classes inherit from task_trees.behavious_base.ConditionalCommanderBehaviour
Class task_trees.behavious_base.SimAttachObject
This class attachs an named object to the end-effector link of the robot.
class SimAttachObject(ConditionalCommanderBehaviour):
def __init__(self, name, condition_fn=True, condition_policy=None, arm_commander=None,
object_name=None, post_fn=None):
...
The parameter post_fn allows the definition of a function that is called after the object is attached to the robot.
Class task_trees.behavious_base.SimDetachObject
This class detach an named object from the end-effector link of the robot.
class SimDetachObject(ConditionalCommanderBehaviour):
def __init__(self, name, condition_fn=True, condition_policy=None, arm_commander=None,
object_name=None, post_fn=None, to_remove=False):
...
If the parameter to_remove is True, the detached object is also removed from the world. This feature is useful in simulation.