This package illustrates an example scenario of a reactive Behavior Tree (BT) implementation. Two actions, "pickup" and "contact" need to be executed in order for a certain task to be executed successfully. To leverage the reactiveness a BT offers, we pair each action with a condition, under a selector node. The conditions will act as the "BT state", which indicate the status of the task.
For instance, if "pickup" was successful, the "has_grasp" condition will be true. When a BT tick is sent, the first subtree will return true, without the need for ticking the pickup action again. If, during the contact action, "has_grasp" becomes false, the tree will react accordingly and preempt "contact". On the following tick, "pickup" will run again.
The demo also implements a service, "/contact/toggle_teach", which when called will toggle between normal and teach modes. In teach mode, the "got_contact" condition will always return false, forcing the tree to repeat the contact action. This illustrates a SARAFun application where we might want to repeat a certain action in order to teach an assembly system details of a task.
After compiling the catkin workspace where the package is downloaded to and sourcing your workspace, run
$ roslaunch contact_nodes contact_nodes.launch to start the system.
You'll have to call a service with the path of the action_nodes_config.yaml path. Example:
$ rosservice call /sarafun/start_tree "file_path: '/home/<username>/catkin_ws/src/contact_nodes/config/example_slippage.json'"
The launch file offers these parameters
debug: Set to true to launch the tree in gdb with the logging level set at debug. Default: falsehas_grasp_fail_thres: Set to a value in the range <0, 1> to define the probability this node will succeed, if the success conditions are met. A value smaller than 1 will showcase the tree reactivity when a grasp is lost. Default: 1
This package depends on the following:
- ROS-Behavior Tree - BT package
- sarafun_bt - Packages which enable integration of generic actionlib servers as actions in a ROS-Behavior Tree.
- sarafun_msgs - Messages used in the examples