ROS2 Integration

Safety middleware for ROS2 robots using THSP (Truth-Harm-Scope-Purpose) validation.

Installation

pip install sentinelseed

# ROS2 packages
sudo apt install ros-humble-rclpy ros-humble-geometry-msgs ros-humble-std-msgs

Architecture

Navigation (nav2) → /cmd_vel_raw → SentinelSafetyNode → Robot
                                          ↓
                                  /sentinel/status

Quick Start

Python Node

import rclpy
from sentinelseed.integrations.ros2 import SentinelSafetyNode

rclpy.init()
node = SentinelSafetyNode(
    input_topic='/cmd_vel_raw',
    output_topic='/cmd_vel',
    max_linear_vel=1.0,
    max_angular_vel=0.5,
    mode='clamp',  # 'block', 'clamp', or 'warn'
)
rclpy.spin(node)

Standalone Filter (No ROS2)

from sentinelseed.integrations.ros2 import (
    CommandSafetyFilter,
    VelocityLimits,
)

filter = CommandSafetyFilter(
    velocity_limits=VelocityLimits.differential_drive(
        max_linear=1.0,
        max_angular=0.5,
    ),
    mode='clamp',
)

safe_twist, result = filter.filter(incoming_twist)

Operating Modes

THSP Gates for Robotics

Truth Gate

• No NaN or infinite values
• No lateral movement on differential drive

Harm Gate

• Velocity exceeds configured limits
• Combined magnitude too high

Scope Gate

• Position within safety zone
• Within operational workspace

Purpose Gate

• Command has justification
• No purposeless spinning

VelocityLimits Presets

from sentinelseed.integrations.ros2 import VelocityLimits

# Differential drive (TurtleBot)
limits = VelocityLimits.differential_drive(max_linear=1.0, max_angular=0.5)

# Omnidirectional (Kuka)
limits = VelocityLimits.omnidirectional(max_linear=1.0, max_angular=0.5)

# Drone/UAV
limits = VelocityLimits.drone(max_linear=2.0, max_vertical=1.0, max_angular=1.0)

SafetyZone

from sentinelseed.integrations.ros2 import SafetyZone

zone = SafetyZone.indoor(room_size=10.0)
# or
zone = SafetyZone(min_x=-10, max_x=10, min_y=-10, max_y=10)

References

• ROS 2 Safety Working Group
• IEC 60204-1 - Stop categories
• ISO 10218 - Robot safety