Software architecture of wheeled mobile robots
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This document summarizes the key aspects of software architecture for wheeled mobile robots. It discusses common architectures including those without an OS, with a real-time OS, and with an embedded OS. It also covers important components like motion control using PID regulators, localization using odometry and lidar, and motion planning algorithms like A* and RRT Connect. The document provides advantages and disadvantages of the different approaches.
Software architecture of wheeled mobile robots
- 1. Software architecture of wheeled mobile robots Dmitry Suvorov
- 2. Index 1. Introduction 2. General software architecture 3. Motion control 4. Localization and mapping 5. Motion planning
- 3. Introduction
- 6. Advantages of differential drive • Simple controlling algorithms; • Good mathematical models of the drive; • Low cost; • Easy prototyping; • No slippage.
- 7. Disadvantages of differential drive • Low permeability of the robot; • Low mobility.
- 9. Types of software architectures • Simple embedded architectures without OS • Architecture based on real-time OS (RTOS) • Architecture based on embedded OS
- 10. Simple embedded architectures without OS Advantages: • Low cost hardware is required • Easy development Disadvantages: • There is no abstraction from hardware. • It is impossible to create to create advanced systems for performing difficult tasks. • Problems with debugging and writing unit tests. Applications: • Toys, research projects.
- 11. Architecture based on real-time OS (RTOS) Advantages: • One processor for high level tasks and hardware control. • Abstraction from hardware level. Disadvantages: • Difficult tasks scheduling. • Difficult logic (high and low tasks are mixed) Applications: • Service robots, military projects and research.
- 12. Architecture based on embedded OS Advantages: • Abstraction from hardware level. • Strong decomposition of tasks on hardware level. • No scheduling problems. • Easy decomposition of tasks between software and hardware developers. Disadvantages: • Higher cost. Applications: • Service robots, toys, military projects and research.
- 13. Typical architecture of the controlling system Decision making Motion planning Motion control Localization SLAM (optionally)
- 14. Motion control
- 15. Tasks • Rotating in place • Following lines • Following arbitrary trajectory
- 16. Automatic control theory Advantages: • Simple well-known theory. • Easy to implement on hardware and software levels. • Can work on slow processors. • There are heuristic methods for tuning parameters. Disadvantages: • It is practically impossible to archive high precision of motion. • It is difficult to calculate parameters of controlling algorithms.
- 17. PID regulator Discrete form: u(t) = P(t) + I(t) + D(t) P(t) = Cp * e(t) I(t) = I(t – T) + Ci * e(t) D(t) = Cd * ( e(t) – e(t-T) ) Cp, Ci, Cd – coefficients of PID regulator; T – period (time between calls of regulator).
- 18. Tuning parameters of PID regulator • P – current error compensation • I – statical error compensation • D - oscillations damping Ziegler–Nichols method: K – coefficient of P-regulator when system become unstable. T – period of oscillations P = 0.6 * K I = 2 * P / T D = P * T / 8
- 19. Robot motion control PID regulator for controlling rotation PD regulator for controlling moving
- 22. Task To control the robot we need to know its real position. Problems: • There is no universal sensor for getting accurate absolute robot position.
- 23. Odometry We can get data from encoders and calculate relative robot position
- 24. Numerical form of odometry
- 25. Odometry Advantages: • No need in additional sensors. Disadvantages: • Low accuracy. • Error increases with time. • High sensitivity to slippage.
- 26. Lidar based localization Advantages: • High accuracy. • Error does not increase with time. • Can be implemented on slow processors. Disadvantages: • Map of the environment is required.
- 27. Methods of localization • Particle filter based. • Kalman filter based.
- 28. Particle filter based localization
- 30. Motion planning
- 31. Task • We need to find path to destination on the map before start of movement. Methods: • Optimal (A*, Dijkstra search …) • Suboptimal (RRT Connect…)
- 32. A* Advantages: • It always finds the shortest way. Disadvantages: • High performance processor is required.
- 33. RRT Connect Advantages: • Very fast. • Can search trajectories in high dimension spaces. Disadvantages: • The found path is not optimal.
- 34. Contacts Dmitry Suvorov d.suvorov90@gmail.com Skoltech Space Robotics Laboratory wicron.com lexybot.com