motion_primitives_controllers

Package to control robots using motion primitives like PTP, LIN and CIRC

Links
C++ API
Standard Documents
- README
- PACKAGE
- CHANGELOG

README

motion_primitive_controllers

Package to control robots using motion primitives like LINEAR_JOINT (PTP/ MOVEJ), LINEAR_CARTESIAN (LIN/ MOVEL) and CIRCULAR_CARTESIAN (CIRC/ MOVEC)

Description

This project provides an interface for sending motion primitives to an industrial robot controller using the ExecuteMotionPrimitiveSequence.action action from control_msgs. The controller receives the primitives via the action interface and forwards them through command interfaces to the robot-specific hardware interface. Currently, hardware interfaces for Universal Robots and KUKA Robots are implemented.

Supported motion primitives:
- LINEAR_JOINT
- LINEAR_CARTESIAN
- CIRCULAR_CARTESIAN

If multiple motion primitives are passed to the controller via the action, the controller forwards them to the hardware interface as a sequence. To do this, it first sends MOTION_SEQUENCE_START, followed by each individual primitive, and finally MOTION_SEQUENCE_END. All primitives between these two markers will be executed as a single, continuous sequence. This allows seamless transitions (blending) between primitives.

The action interface also allows stopping the current execution of motion primitives. When a stop request is received, the controller sends STOP_MOTION to the hardware interface, which then halts the robot’s movement. Once the controller receives confirmation that the robot has stopped, it sends RESET_STOP to the hardware interface. After that, new commands can be sent.

Action Image

This can be done, for example, via a Python script as demonstrated in the example python script in the Universal_Robots_ROS2_Driver package.

Command and State Interfaces

To transmit the motion primitives, the following command and state interfaces are required. All interfaces use the naming scheme tf_prefix_ + "motion_primitive/<interface name>" where the tf_prefix is provided to the controller as a parameter.

Command Interfaces

These interfaces are used to send motion primitive data to the hardware interface:

motion_type: Type of motion primitive (LINEAR_JOINT, LINEAR_CARTESIAN, CIRCULAR_CARTESIAN)
q1 – q6: Target joint positions for joint-based motion
pos_x, pos_y, pos_z: Target Cartesian position
pos_qx, pos_qy, pos_qz, pos_qw: Orientation quaternion of the target pose
pos_via_x, pos_via_y, pos_via_z: Intermediate via-point position for circular motion
pos_via_qx, pos_via_qy, pos_via_qz, pos_via_qw: Orientation quaternion of via-point
blend_radius: Blending radius for smooth transitions
velocity: Desired motion velocity
acceleration: Desired motion acceleration
move_time: Optional duration for time-based execution (For LINEAR_JOINT and LINEAR_CARTESIAN. If move_time > 0, velocity and acceleration are ignored)

State Interfaces

These interfaces are used to communicate the internal status of the hardware interface back to the motion_primitives_forward_controller.

execution_status: Indicates the current execution state of the primitive. Possible values are:
- IDLE: No motion in progress
- EXECUTING: Currently executing a primitive
- SUCCESS: Last command finished successfully
- ERROR: An error occurred during execution
- STOPPING: The hardware interface has received the STOP_MOTION command, but the robot has not yet come to a stop.
- STOPPED: The robot was stopped using the STOP_MOTION command and must be reset with the RESET_STOP command before executing new commands.
ready_for_new_primitive: Boolean flag indicating whether the interface is ready to receive a new motion primitive