Admittance Controller

Admittance controller enables you do zero-force control from a force measured on your TCP. The controller implements ChainedControllerInterface, so it is possible to add another controllers in front of it, e.g., JointTrajectoryController.

The controller requires an external kinematics plugin to function. The kinematics_interface repository provides an interface and an implementation that the admittance controller can use.

ROS 2 interface of the controller

Parameters

The admittance controller uses the generate_parameter_library to handle its parameters. The parameter definition file located in the src folder contains descriptions for all the parameters used by the controller.

An example parameter file for this controller can be found in the test folder:

Topics

~/joint_references (input topic) [trajectory_msgs::msg::JointTrajectoryPoint]

Target joint commands when controller is not in chained mode.

~/wrench_reference (input topic) [geometry_msgs::msg::WrenchStamped]

Target wrench offset (WrenchStamped has to be in the frame of the FT-sensor).

~/state (output topic) [control_msgs::msg::AdmittanceControllerState]

Topic publishing internal states.

ros2_control interfaces

References

The controller has position and velocity reference interfaces exported in the format: <controller_name>/<joint_name>/[position|velocity]

States

The state interfaces are defined with joints and state_interfaces parameters as follows: <joint>/<state_interface>. Supported state interfaces are position, velocity, and acceleration as defined in the hardware_interface/hardware_interface_type_values.hpp. If some interface is not provided, the last commanded interface will be used for calculation.

For handling TCP wrenches *Force Torque Sensor* semantic component (from package *controller_interface*) is used. The interfaces have prefix ft_sensor.name, building the interfaces: <sensor_name>/[force.x|force.y|force.z|torque.x|torque.y|torque.z].

Commands

The command interfaces are defined with joints and command_interfaces parameters as follows: <joint>/<command_interface>. Supported state interfaces are position, velocity, and acceleration as defined in the hardware_interface/hardware_interface_type_values.hpp.