DVZ (Deformable Virtual Zone)

DVZ (Deformable Virtual Zone)#

The DVZ is a reactive motion control method first introduced by R. Zapata in 1994 [1]. It has been used since to model systems’ maneuvers in both 2D and 3D spaces. The idea is to surround the system under study with a virtual zone, and any body entering that zone will cause a deformation. Then, the system can be driven in the direction minimizing this deformation or changing it in a desired way.

Supported Motion Models#

  • ACKERMANN

  • DIFFERENTIAL_DRIVE

  • OMNI

Supported Sensory Inputs#

  • LaserScan

Implementation#

  • Define a circular zone around the robot with known undeformed radius ($\(R\)$)

  • Using LaserScan sensor data compute the deformed radius: \( d_h(\alpha) : \alpha in [0, 2\pi]\)

  • Compute the zone deformation:

\( I_D = \frac{1}{2\pi} \int_{0}^{2\pi}\frac{R - d_h(\alpha)}{R} d\alpha \in [0, 1]\)

  • Compute the zone deformation radius (if \(I_D > 0\)):

\( \Theta_D = \frac{\int_{0}^{2\pi} (R - d_h(\alpha))\alpha d\alpha}{I_D} \in [0, 2\pi]\)

  • The control is calculated to minimize \(I_D\) and stay close to the reference trajectory

Parameters and Default Values#

Name

Type

Default

Description

min_front_margin

float

1.0

Minimum front margin distance. Must be between 0.0 and 1e2.

K_linear

float

1.0

Proportional gain for linear control. Must be between 0.1 and 10.0.

K_angular

float

1.0

Proportional gain for angular control. Must be between 0.1 and 10.0.

K_I

float

5.0

Proportional deformation gain. Must be between 0.1 and 10.0.

side_margin_width_ratio

float

1.0

Width ratio between the deformation zone front and side (circle if 1.0). Must be between 1e-2 and 1e2.

heading_gain

float

0.7

Heading gain of the internal pure follower control law. Must be between 0.0 and 1e2.

cross_track_gain

float

1.5

Gain for cross-track error of the internal pure follower control law. Must be between 0.0 and 1e2.

usage Example#

DVZ algorithm can be used in the Controller component by setting ‘algorithm’ property or component config parameter. The Controller will configure DVZ algorithm using the default values of all the previous configuration parameters. To configure custom values of the parameters, a YAML file is passed to the component.

dvz.py#
from kompass.components import Controller, ControllerConfig
from kompass.robot import (
    AngularCtrlLimits,
    LinearCtrlLimits,
    RobotCtrlLimits,
    RobotGeometry,
    RobotType,
    RobotConfig
)
from kompass.control import LocalPlannersID

# Setup your robot configuration
my_robot = RobotConfig(
    model_type=RobotType.ACKERMANN,
    geometry_type=RobotGeometry.Type.BOX,
    geometry_params=np.array([0.3, 0.3, 0.3]),
    ctrl_vx_limits=LinearCtrlLimits(max_vel=0.2, max_acc=1.5, max_decel=2.5),
    ctrl_omega_limits=AngularCtrlLimits(
        max_vel=0.4, max_acc=2.0, max_decel=2.0, max_steer=np.pi / 3)
)

# Set DVZ algorithm using the config class
controller_config = ControllerConfig(algorithm="DVZ")  # or LocalPlannersID.DVZ

# Set YAML config file
config_file = "my_config.yaml"

controller = Controller(component_name="my_controller",
                        config=controller_config,
                        config_file=config_file)

# algorithm can also be set using a property
controller.algorithm = LocalPlannersID.DVZ      # or "DVZ"
my_config.yaml#
my_controller:
  # Component config parameters
  loop_rate: 10.0
  control_time_step: 0.1
  ctrl_publish_type: 'Sequence'

  # Algorithm parameters under the algorithm name
  DVZ:
    cross_track_gain: 1.0
    heading_gain: 2.0
    K_angular: 1.0
    K_linear: 1.0
    min_front_margin: 1.0
    side_margin_width_ratio: 1.0