Unilateral Control

This section describes how to run unilateral control using the provided scripts

💡 Project Architecture Summary

The project uses a multi-threaded structure.

A custom class derived from PeriodicTimerThread is used to spawn and manage three threads:

• Leader thread: Handles control logic for the leader arm.
• Follower thread: Handles control logic for the follower arm.
• Admin thread: Manages coordination and communication between components.

Core control logic is encapsulated in the Control class, which supports both:

• Bilateral control: For force-feedback, master-slave style interaction.
• Unilateral control: For single-arm or open-loop operation without feedback.

Control & Friction Parameters (per joint)

Name	Meaning
Dn	Damping in the controller (velocity-based)
Jn	Nominal inertia (used in observers)
gn	Cut-off frequency for observers
Kp	Position control gain
Kd	Velocity control gain
Kf	Force control gain
Fc	Static friction (Coulomb) level
k	Sharpness of friction transition
Fv	Viscous friction (speed-based)
Fo	Friction offset (bias correction)

tip

In unilateral control, only the friction parameters (Fc, k, Fv, Fo) are used. The control gains and observer parameters are not required.

Friction Model

The following tanh-based model is used for friction compensation:

tau_f = Fc * tanh(k * dq) + Fv * dq + Fo

Running the Script

cd openarm_teleop
./script/launch_unilateral.sh right_arm can0 can1

Arguments

• right_arm or left_arm: Specifies which arm to use.
• can0: CAN interface for the leader arm.
• can1: CAN interface for the follower arm.

If the CAN interfaces are omitted, the script uses the following defaults:

• For right_arm: leader = can0, follower = can1
• For left_arm: leader = can2, follower = can3

What the Script Does

1. Validates the arm side (right_arm or left_arm).
2. Sets default CAN interfaces if not specified.
3. Generates temporary URDFs for the leader and follower using xacro.
4. Launches the unilateral control binary with appropriate arguments.
5. Cleans up temporary files after execution.

File Paths Used

• Xacro file: ~/openarm_ros2_ws/src/openarm_description/urdf/robot/v10.urdf.xacro
• Generated URDFs: /tmp/openarm_urdf_gen/{v10_leader.urdf, v10_follower.urdf}
• Binary: ~/openarm_teleop/build/unilateral_control

Important Notes for Unilateral Control

• The zero position of the arm is defined as the posture where the arm is lowered straight down. Make sure the robot is in this position before starting control.

• Unlike bilateral control, unilateral control does not provide force feedback. Be cautious when making contact with objects, as unexpected forces will not be reflected to the operator.