Activity Diagram of Elevator System

Objective:

This activity diagram models the flow of operations in the elevator system when a passenger requests an elevator and selects a destination. It covers the complete lifecycle of a single ride, from request to drop-off, including decision points and concurrent activities.

Activity Flow Description:

• Start
  The system is idle, waiting for a user interaction.

• User Presses Floor Call Button (Up/Down)
  A passenger presses the button on their current floor, indicating they want to go up or down.

• Send Request to Elevator Controller
  The request is sent to the central Elevator Controller, which manages all active elevators.

• Controller Checks Elevator Availability
  The controller checks for:

  • Nearest idle elevator

  • Elevator moving in the same direction

  • Load capacity and current state

• Assign Elevator
  Based on scheduling logic (e.g., nearest car, least busy, etc.), the controller assigns an elevator.

• Elevator Moves to User’s Floor
  The assigned elevator begins to move toward the requesting floor.

• Elevator Arrives and Door Opens
  Once the elevator reaches the user’s floor, it stops, opens the door, and waits for the passenger to enter.

• Passenger Enters and Selects Destination Floor
  The passenger uses the button panel inside the elevator to select the desired floor.

• Elevator Starts Moving to Destination
  The elevator processes the floor request and starts moving toward the selected floor.

• Elevator Monitors Load and Emergency Conditions
  While in motion, the system continuously checks:
• Weight sensors
• Emergency signals (fire, power loss, etc.)
• Obstruction detection

• Elevator Reaches Destination Floor
  The elevator stops at the selected floor.

• Door Opens and Passenger Exits
  The door opens automatically, and the user exits the elevator.

• Door Closes Automatically After Timeout or Sensor Trigger
  Once the passenger exits, the door closes if no obstruction is detected.

• Elevator Updates State and Becomes Idle/Handles Next Request
  The elevator either becomes idle or proceeds to the next queued request.

• End of Activity
  The cycle is complete, and the system is ready for the next request.

Diagram Elements You Can Draw (for class presentation):

• Initial Node: Black circle indicating start.

Activity Nodes:

• “User presses call button”
• “Controller assigns elevator”
• “Elevator moves to floor”
• “Door opens”
• “User enters and selects floor”
• “Elevator moves to destination”
• “User exits”

Decision Nodes:

• Elevator available?
• Emergency detected?
• Floor reached?

• Synchronization Bars (fork/join): For door open and sensor check to happen concurrently.

• Final Node: Solid black circle inside another circle, indicating end of activity.