Finite State Machines: Part 1

Summary

The video explains how a home cleaning robot operates using a finite state machine (FSM) model. The robot starts in a 'wandering' state, detects obstacles, spins to clean dirty spots, and returns to its charger when the battery is low. These actions are represented as states and transitions in the FSM, with valid sequences leading the robot to its 'off' state. The script showcases how various event strings trigger state changes and highlights the importance of proper transitions in ensuring the robot completes its cleaning tasks.

Takeaways

• 🤖 The robot cleans by wandering around a room and responds to obstacles by turning, then resumes wandering.
• 🧹 If the robot encounters a dirty spot, it stops, spins in place to clean the area, and then returns to wandering.
• 🔋 When the battery runs low, the robot makes a direct path back to its home charger and shuts off.
• 📊 The robot's behavior can be represented as a finite state machine (FSM), a graph with states and transitions.
• 🔄 The robot starts in a 'Wandering' state (W) and transitions to a 'Turning' state (T) when it hits an obstacle.
• 🌀 When dirt is detected, the robot enters a 'Spinning' state (S), transitioning back to 'Wandering' when the spot is clean.
• 🏠 When the battery is low ('b'), the robot enters the 'Go Home' state (G), eventually reaching the 'Off' state (F) when it returns to its charger.
• 🔗 States and transitions are labeled simply: 'o' for obstacle, 'r' for resume, 'd' for dirty, 'n' for clean, 'b' for low battery, 'h' for home, and 'F' for off.
• ✅ A valid sequence of events, such as 'orbh', leads the robot from wandering to turning, resuming, going home, and shutting off.
• ❌ Invalid sequences, like 'ordnrbh', fail because they do not follow the correct state transitions as defined in the FSM.

Q & A

What is a finite state machine as described in the script?

A finite state machine is a directed graph consisting of states (vertices) and transitions (edges) between those states. It begins at an initial state and moves through states based on inputs until it potentially reaches an accepting state.

How does the robot transition between states when it encounters an obstacle?

When the robot encounters an obstacle, it transitions from the 'wandering' state (W) to the 'turning' state (T). Once the obstacle is cleared, it returns to the 'wandering' state.

What happens when the robot detects a dirty spot?

When the robot detects a dirty spot, it enters the 'spin' state (S) where it spins in place to clean the area. Once the spot is clean, it returns to the 'wandering' state.

What does the robot do when its battery is low?

When the robot’s battery is low, it transitions from its current state to the 'go home' state (G) and moves directly to its charging station. Upon arrival, it turns itself off, entering the 'F' state.

What symbols are used to represent different states and transitions in the finite state machine for the robot?

The states are labeled as follows: 'W' for wandering, 'T' for turning, 'S' for spin, 'G' for go home, and 'F' for off. Transitions are labeled with symbols like 'o' for obstacle, 'r' for clear, 'd' for dirty, 'n' for clean, 'b' for low battery, and 'h' for home.

What is an example of a valid sequence of events for the robot's cleaning process?

An example of a valid sequence is 'orbh'. The robot transitions from 'W' to 'T' with 'o', back to 'W' with 'r', then to 'G' with 'b', and finally to 'F' with 'h'.

What happens if the robot receives a low battery warning while in the spin state?

If the robot receives a low battery warning while in the spin state (S), it immediately transitions to the 'go home' state (G) to return to its charging station.

Why was the string 'oordbh' accepted in the simulator?

The string 'oordbh' was accepted because it follows valid transitions based on the state machine diagram, including transitioning from the spin state directly to the go home state when a low battery warning is received.

Why was the string 'ordnrbh' not accepted in the simulator?

The string 'ordnrbh' was not accepted because there was no transition defined from the wandering state (W) when the 'clear' event ('r') occurs, making it an invalid sequence.

How does the finite state machine determine if a string of events is accepted?

The finite state machine evaluates the string of events from left to right, starting at the initial state. If it reaches the accepting state ('F') when the last symbol in the string is consumed, the string is considered accepted.