/control/command/control_cmd#

Specifications#

Description#

Send the control command to the vehicle. This is the command format that can be used universally in vehicles based on the Ackermann kinematic model. At this stage, do not expect anything other than simple control such as smoothly approaching the target value. For example, the time-series control involving acceleration and deceleration to reach a target speed must have been completed in a previous stage. Therefore, it is generally assumed that the target value will be sent at a time close enough that linear interpolation is possible. If your vehicle interface would like to support time series data directly, please join the discussion of the ControlHorizon message.

The autoware_component_interface_specs package defines this topic with volatile durability. In the default launch of Autoware, the autoware_vehicle_cmd_gate node publishes this topic with transient_local durability. volatile subscribers also receive its messages. Make sure that the publishers and the subscribers in your system use compatible QoS settings.

Message#

For details about the message, see the readme of autoware_control_msgs.

The velocity, acceleration, and jerk values at a given time must be planned in advance and must be consistent, which is typically done by the planning/control component. If these values are inconsistent, which value takes priority depends on the vehicle implementation.

Sending the latest command will invalidate previous commands, which means that commands from different time stamps are not kept as a time series. Only the latest command, not the latest time stamp command, is valid.

Errors#

Command Timeout: If the command is not sent frequently enough to control the current vehicle speed, the vehicle executes an emergency stop.

Out of Range: If the command exceeds the given physical limit, the value is clamped to the maximum.

Support#

This interface is required. If there is only a vehicle-specific interface, provide a converter. For vehicles controlled by typical accelerator and brake pedals, consider using the autoware_raw_vehicle_cmd_converter.

Limitations#

Command filter: The commands may be filtered by a rate limiter to prevent physically impossible or unsafe rapid acceleration or steering.

Use cases#

• Control the vehicle for autonomous driving.
• Relay commands from the operator.

Requirement#

• Support sending the control command to the vehicle.
• Ignore the control command depending on the control mode.
• Report the error as diagnostics in the following cases:
  • Topic rate is too low or too high.
  • An unacceptable target value is sent.
  • It fails to achieve the target value.

Design#

Topic rate: In Autoware 2.0.0, the controller sets the rate of this topic. autoware_trajectory_follower_node calculates a command on a timer with the period ctrl_period. The trajectory_follower_node.param.yaml file of autoware_launch sets ctrl_period: 0.03, which gives about 33 Hz. autoware_vehicle_cmd_gate publishes each command that it receives on this topic immediately, so this topic has the same rate. The gate also has a timer with update_rate: 10.0 in vehicle_cmd_gate.param.yaml. This timer publishes the gear, turn indicator, and hazard light commands. It publishes a stop command on this topic only when the system emergency heartbeat times out or when an external emergency stop is active.

Basis for the rate: The controllers use ctrl_period as their time step. For example, the MPC lateral controller rounds the steering delay to a whole number of control periods, and it limits the steering change in each period. The mpc.param.yaml file sets the steering delay to 0.24 s (input_delay) and the steering time constant to 0.27 s (vehicle_model_steer_tau). The period of 0.03 s is much shorter than these values. As a result, the controller corrects the command several times while the steering responds. If you change ctrl_period, the controller behavior also changes.

Rate diagnostics: The topic_state_monitor_control_command_control_cmd node of autoware_topic_state_monitor monitors this topic. The topics.yaml file sets warn_rate: 5.0, error_rate: 1.0, and timeout: 1.0. The status becomes a warning below 5 Hz. It becomes an error below 1 Hz or when no message arrives for 1 s. The control.yaml diagnostic graph reports this status as /autoware/control/topic_rate_check/control_command. These limits are much lower than the normal rate, so they find a controller that stopped or became very slow. The monitor does not find a rate that is too high.

History#