Docking Server

Source code on Github.

The Docking Server in opennav_docking implements a server for docking and undocking a robot. This can be from Charging stations (i.e. docks) or non-charging docking locations such as the end of a conveyor belt or a pallet. It uses plugin dock implementations for a particular platform to enable the framework to generalize to robots of many different kinematic models, charging methods, sensor modalities, charging-type, and so on. It can also handle a database of many different docking locations and dock models to handle a heterogeneous environment. This task server is designed be called by an application BT or autonomy application to dock once completed with tasks or battery is low – not within the navigate-to-pose action itself (though undock may be called from inside navigate actions!).

Thanks to NVIDIA for sponsoring this Docking Server package!

Parameters

controller_frequency

Type	Default
double	50.0

Description: Control frequency (Hz) for vision-control loop.

initial_perception_timeout

Type	Default
double	5.0

Description: Timeout (s) to wait to obtain initial perception of the dock.

wait_charge_timeout

Type	Default
double	5.0

Description: Timeout (s) to wait to see if charging starts after docking.

dock_approach_timeout

Type	Default
double	30.0

Description: Timeout (s) to attempt vision-control approach loop.

undock_linear_tolerance

Type	Default
double	0.05

Description: Tolerance (m) to exit the undocking control loop at staging pose.

undock_angular_tolerance

Type	Default
double	0.05

Description: Angular Tolerance (rad) to exist undocking loop at staging pose.

max_retries

Type	Default
int	3

Description: Maximum number of retries to attempt.

base_frame

Type	Default
string	“base_link”

Description: Robot’s base frame for control law.

fixed_frame

Type	Default
string	“odom”

Description: Fixed frame to use, recommended to be a smooth odometry frame not map.

dock_backwards

Type	Default
bool	false

Description: Whether the robot is docking with the dock forward or backward in motion.

dock_prestaging_tolerance

Type	Default
double	0.5

Description: L2 distance in X,Y,Theta from the staging pose to bypass navigation.

dock_plugins

Type	Default
vector<string>	N/A

Description: A set of dock plugins to load.

dock_database

Type	Default
string	N/A

Description: The filepath to the dock database to use for this environment. Use docks or this param.

docks

Type	Default
vector<string>	N/A

Description: Instead of dock_database, the set of docks specified in the params file itself. Use dock_database or this param.

navigator_bt_xml

Type	Default
string	“”

Description: BT XML to use for Navigator, if non-default.

controller.k_phi

Type	Default
double	3.0

Description: Ratio of the rate of change of angle relative to distance from the target. Much be > 0.

controller.k_delta

Type	Default
double	2.0

Description: Higher values result in converging to the target more quickly.

controller.beta

Type	Default
double	0.4

Description: Parameter to reduce linear velocity proportional to path curvature. Increasing this linearly reduces the velocity (v(t) = v_max / (1 + beta * |curv|^lambda)).

controller.lambda

Type	Default
double	2.0

Description: Parameter to reduce linear velocity proportional to path curvature. Increasing this exponentially reduces the velocity (v(t) = v_max / (1 + beta * |curv|^lambda)).

controller.v_linear_min

Type	Default
double	0.1

Description: Minimum velocity for approaching dock.

controller.v_linear_max

Type	Default
double	0.24

Description: Maximum velocity for approaching dock.

controller.v_angular_max

Type	Default
double	0.75

Description: Maximum angular velocity for approaching dock.

controller.slowdown_radius

Type	Default
double	0.25

Description: Radius to end goal to commense slow down.

Note: dock_plugins and either docks or dock_database are required.

SimpleChargingDock Parameters

Simple Charging Dock is a provided charging dock plugin that can handle many docks and common techniques.

<dock_name>.staging_x_offset

Type	Default
double	-0.7

Description: Staging pose offset forward (negative) of dock pose (m).

<dock_name>.staging_yaw_offset

Type	Default
double	0.0

Description: Staging pose angle relative to dock pose (rad).

<dock_name>.use_battery_status

Type	Default
bool	true

Description: Whether to use the battery state message or isDocked() for isCharging().

<dock_name>.use_external_detection_pose

Type	Default
bool	false

Description: Whether to use external detection topic for dock or use the databases’ pose.

<dock_name>.external_detection_timeout

Type	Default
double	1.0

Description: Timeout (s) at which if the newest detection update does not meet to fail.

<dock_name>.external_detection_translation_x

Type	Default
double	-0.20

Description: X offset from detected pose for docking pose (m).

<dock_name>.external_detection_translation_y

Type	Default
double	0.0

Description: Y offset from detected pose for docking pose (m).

<dock_name>.external_detection_rotation_yaw

Type	Default
double	0.0

Description: Yaw offset from detected pose for docking pose (rad).

<dock_name>.external_detection_rotation_pitch

Type	Default
double	1.57

Description: Pitch offset from detected pose for docking pose (rad). Note: The external detection rotation angles are setup to work out of the box with Apriltags detectors in image_proc and isaac_ros.

<dock_name>.external_detection_rotation_roll

Type	Default
double	-1.57

Description: Roll offset from detected pose for docking pose (rad). Note: The external detection rotation angles are setup to work out of the box with Apriltags detectors in image_proc and isaac_ros.

<dock_name>.filter_coef

Type	Default
double	0.1

Description: Dock external detection method filtering algorithm coefficient.

<dock_name>.charging_threshold

Type	Default
double	0.5

Description: Threshold of current in battery state above which isCharging() = true.

<dock_name>.use_stall_detection

Type	Default
bool	false

Description: Whether or not to use stall detection for isDocked() or positional threshold.

<dock_name>.stall_joint_names

Type	Default
vector<string>	N/A

Description: Names in joint_states topic of joints to track.

<dock_name>.stall_velocity_threshold

Type	Default
double	1.0

Description: The joint velocity below which to trigger isDocked() = true.

<dock_name>.stall_effort_threshold

Type	Default
double	1.0

Description: Current or motor effort in joint state to trigger isDocked() = true.

<dock_name>.docking_threshold

Type	Default
double	0.05

Description: If not using stall detection, the pose threshold to the docking pose where isDocked() = true.

Example

docking_server:
  ros__parameters:
    controller_frequency: 50.0
    initial_perception_timeout: 5.0
    wait_charge_timeout: 5.0
    dock_approach_timeout: 30.0
    undock_linear_tolerance: 0.05
    undock_angular_tolerance: 0.1
    max_retries: 3
    base_frame: "base_link"
    fixed_frame: "odom"
    dock_backwards: false
    dock_prestaging_tolerance: 0.5

    # Types of docks
    dock_plugins: ['nova_carter_dock']
    nova_carter_dock:
      plugin: 'opennav_docking::SimpleChargingDock'  # Also 'opennav_docking::SimpleNonChargingDock'
      docking_threshold: 0.05
      staging_x_offset: -0.7
      use_external_detection_pose: true
      use_battery_status: false # true
      use_stall_detection: false

      external_detection_timeout: 1.0
      external_detection_translation_x: -0.18
      external_detection_translation_y: 0.0
      external_detection_rotation_roll: -1.57
      external_detection_rotation_pitch: -1.57
      external_detection_rotation_yaw: 0.0
      filter_coef: 0.1

    # Dock instances
    docks: ['home_dock']
    home_dock:
      type: 'nova_carter_dock'
      frame: map
      pose: [0.0, 0.0, 0.0]
      id: 'c67f50cb-e152-4720-85cc-5eb20bd85ce8'

    controller:
      k_phi: 3.0
      k_delta: 2.0
      v_linear_min: 0.15
      v_linear_max: 0.15